Fun punishments should never be used in response to something you don't want your sub to do. Likewise, they should only be used in a manner that your sub will know is playful. This doesn't mean you can't role play a fun punishment as if it were a real punishment, but even if you're acting otherwise, it should only be done with things that you are obviously not really upset about. For example, when my pet is massaging my legs and thighs (all the way up please) I might tell him if he gets hard I'll have to punish him with a spanking, or make him go down on me, etc. It doesn't even have to make sense. You can pick pretty much anything you two enjoy for a fun punishment and any excuse to exact said punishment. All you have to do is act like it's a punishment; tell him he's been a naughty boy and must suffer with the consequences. This sort of "discipline" is a lot of fun and you can find countless great ideas online.
However, the topic often overlooked is real punishment, and that's what I'd like to focus on. This is part of what's often called domestic discipline. The goal with domestic discipline is usually behavioral change and it can be achieved. To me, this is one of the most overlooked perks of being a dominant in a serious D/s relationship. It allows you to changes things about your partner that you could only complain about in a vanilla relationship. Most subs love the whole "training" aspect, but even those who don't fantasize about it are often still turned on by the idea. You get a well behaved sub and they get what they enjoy, being treated like your pet. So even with real punishments, both sides enjoy the power exchange.
One thing to keep in mind when dealing with real punishments is to avoid discipline that's difficult or hard on you. If something is a lot of trouble, then it's also a punishment for you. The exception of course is if it's something you really enjoy, then it becomes a labor of love. Perhaps you really enjoy pegging and your guy hates it, then this is still an acceptable punishment for serious infractions. But most men love pegging and a good amount of women don't get much enjoyment from it. So, again, be careful with what you use as a punishment. Don't let your sub trick you into using a fun punishment in the place of a real one! Due to the power exchange involved in being disciplined, it's normal for the thought or act of discipline to turn your sub on. Any punishment has the potential to make a submissive more horny, and there's nothing wrong with this as long as the punishment itself isn't something he enjoys or looks forward to.
The most important thing I've learned over the years is that real punishments in a femdom dynamic should always have a sexual element to them. You don't want your sub to be angry with you about being punished. Having a sexual element involved connects to him on a low, submissive, sexual level, and reminds him that training is something he wants as well. This association will also help your sub accept his punishment and negate any resentment, even when he feels he's being punished unfairly. If purely sexual punishments don't work for you, it's also fairly easy to add a sexual element to otherwise normal punishments. For example, one vanilla punishment might be standing in the corner for 15 minutes. To add a sexual element to this, have your sub wear weights from his balls
I've had the most success and happiest subs with punishments that are entirely sexual in nature. My personal favorite is ball spankings. I like the term "spanking" because it even sounds harsh. It's the punishment I most commonly give my husband for breaking any of the "pet rules." The pet rules started out as a list of my pet peeves, pun intended, but I've since added other offenses to the list, such as not getting the door for me and leaving the lights on when he leaves a room. When he breaks a pet rule, I let him know as soon as possible that he will be getting a ball spanking for the infraction. This can be tricky when it happens in public but do try to mention it as soon as possible in case your sub didn't realize his transgression. If, by the end of the day, he's earned any punishment, I'll tell him to get himself ready for his ball spanking. This means he is to undress, secure himself to the bed, and wait for me. If he is hard, I wait until he's not hard. I like to hold his balls with one hand while I spank with the other so it's more like a spanking and less like a slapping. When we begin I ask him what he did wrong, if I have to remind him then he's earned extra! You want him thinking about what he did and to associate it with the punishment. While fixed punishments work, I like to give myself discretion in deciding the actual number of spankings. I start with a few spanks for a first time offense and increase it each time it happens, possibly decreasing back down if he hasn't broken the rule lately. How many will vary from sub to sub depending not only on their tolerance but how hard you spank. Make him count each spank out loud, an extra if he doesn't count quickly enough. With pets new to this you'll have to tell them what to do every step of the way, but they learn quickly, especially if you give them an extra spank for needing to be reminded. All you should need to say is, "go get ready for your ball spanking."
This brings up the second most important part of a proper punishment: Ritual. Since the term punishment is used both playfully and seriously in the community, it's absolutely paramount that your sub knows when he's really being punished. As I've mentioned before, I'm not big a fan of protocol, but this is one situation that really should have an "official" procedure. Unlike most protocol, this serves a very specific purpose. You don't want any uncertainty between what's a real punishment and what isn't. Your sub should never be confused over whether he's being punished or not! (And trust me, nothing feels worse than finding out your sub thought he was being punished when you were only playing.) With a protocol in place, your sub will know for certain that you are unhappy with what he did. Having a set procedure also serves to build up to the punishment and effectively draws it out. This not only gives the sub more time to regret and reflect on what he's done wrong, but it makes the punishment more memorable. This helps the effectiveness of training.
Despite the advantages it provides, I've found that over time it's easy to let parts of your ritual slip. To you it may seem like nothing, but subs often interpret this to mean you don't care as much. Worse, the entire ritual can eventually fall by the side and now your sub will be even more easily confused if he's in trouble or not - having the opposite effect we first intended. Other than just being vigilant about the process, I've found the trick is to leave any preparation to your sub. In my case I have my sub not only undress, but cuff his ankles to either corner of the bed and his hands together over his head with the cuffs looping around the frame of the headboard. This approach not only makes it easier on you, which I'm all about, but is a great way of keeping your ritual. If your sub forgets something, a little extra punishment will help him remember the next time and it eventually becomes habit.
Since I'm on the topic of CBT or ballbusting as a punishment, I just want to interject a warning. This is a popular fetish among submissive men so it's important to be careful your sub isn't enjoying it more than he's disliking it. There are two kinds of masochistic subs. Those who get harder from pain, or prefer they are hard during it, and those that will go soft from pain, or don't mind being soft during it. I think most tops prefer guys from the first group, but there are a lot out there from the second. Those from the second category make painful punishment a little more tricky. With any kind of pain play you typically start light and work your way up. The endorphins build up slowly and your sub can enjoy more and more pain. The trick with any kinky punishment is to administer it before the endorphins kick in. You can usually get a really good pain response from your sub without going further - or much further - than you would during normal play time! And there's no added risk of injury in such a situation. I've seen people who play harder with their pets than they punish them because the sub has a much more subdued reactions during playtime where pain builds up over time. It can be a mental block for some tops and I understand the concern that you might go too far, especially if you don't have a lot of experience yet. That said - going back to the recommended punishment of ball spanking - balls can take a lot of abuse. You can be rather rough with them without doing lasting damage. In fact it takes less pressure to break a rib than to rupture a testicle. So the strategy is simple. Don't start slowly. Do it fast and do it hard. If he's getting an erection then stay ahead of the endorphin curve and hit him harder. I even have a friend who will intentionally get her sub hard and then spank his balls until he goes soft. Just remember, balls can take a lot. Don't be nice, be serious. Here's an example where the sub counts out 50 spankings. And for the more dedicated, here's an example of a 1 minute spanking with a padded paddle where the sub is gagged.
Another real punishment I often use with my hubby is orgasm denial followed by a ruined orgasm, particularly in the case where he comes when he's not allowed. While certainly not a necessary component, I do feel it fits the crime. He doesn't enjoy going week(s) without being allowed to come, and he knows the resulting orgasm won't be any good after all that build up so it works as a serious punishment. With different subs you'll need different amounts of time to get the same effect. With some, it won't work at all, and with others you may find a ruined orgasm at the end of regular play session is effective on it's own. Just make sure he knows it's coming and make sure he knows it's meant as a punishment; again, think ritual! Make him tell you why he's being punished, be clinical about it, etc. Also, because denial is a punishment that occurs over a period of time, I have him tell me why he is not allowed to come each time there's a missed opportunity. During such punishments I like to make my subs masturbate more, and will make excuses to play with them just so they have to tell me why they are being denied. The repetition really helps prevent repeat offenses.
Dealing with a sub in orgasm denial can be tricky as well. Some subs will ask or even beg for less time in orgasm denial. Ironically, I find these are often the ones who've fantasized about it the most. It often turns out they like the fantasy more than the reality of it. If your sub starts asking for a reduced sentence, add a day. They learn quickly, and trust me, it can get on your nerves fast. If a sub isn't asking for less time, but is still complaining, make a rule that any complaint related to punishment must include a thank you, or you'll add a day. I do both of these things and it makes orgasm denial much easier to administer. If he comes during this punishment due to a fault of his own, then we start over and his cock isn't allowed any physical stimulation. But I'm lenient here because this kind of inactive denial can have a huge emotional effect. I can also admit when I'm partially to blame, especially if he warned me he was close. In those cases we simply start the denial period over again. If it happened at his own hands I like to double the time.
I've had other pets in the past who would intentionally make trouble when I announced this was the punishment. You may be surprised how men who love their orgasm so much will want to not have one so badly, but it's often about the fantasy. As I mentioned earlier, when actually playing they almost always want that orgasm. When it comes down to it, many realize it's not what they really wanted, and they regret making trouble. What they really want is for you to take control of their orgasms as part of your control over them. (Which I suggest you do anyway.) The lesson here? Some subs fantasize about punishments they'll actually hate. So don't rule out a punishment just because your sub has fantasized about it in the past. In the same vein, don't be angry if they test you on any new punishment or rule, but be sure to follow through! There's no fixed set of what works as a deterrent. You just have to try things out and see if behavior improves. If things are actually getting worse then it's most likely your sub is enjoying the punishment too much. Don't be afraid to step up the intensity of a punishment your sub may be enjoying to see if that helps, though you may have to try something different if you aren't getting the results you want.
Getting started is easier than you'd think. I suggest sitting down with your sub and establishing some rules so he knows what he'll be punished for. In heavier power exchange relationships it's not uncommon to reserve the right to punish the sub for things that aren't on the list, but especially in new relationships, a formal list will help set expecations for your sub. This will also help you remember what rules you are enforcing. As for some examples of the type of things you can fix, here are a couple of my pet peeves: the toilet left up, an empty toilet paper roll, clothes not in the laundry basket, towels on the floor, plates not in the sink, trash next to the garbage bin, and trash not taken out on trash day. I suggest adding anything that bothers you. All the rules don't have to be serious either, some can be fun. I have a bigger list of rules here if you want more ideas. When he does something wrong, you will get the best results if you punish him as soon as possible so he associates it with the punishment. Alternatively, some people will pick a particular day of the week to take care of punishments. If you prefer to wait, or have to because others are around, do your best to point out transgressions to him at the time they happen. Either way, always ask him why he's being punished when you are about to punish him; you want him thinking about what he did wrong when he's being punished.
To review, a good punishment should be sexual in nature or at the very least have a strong sexual element to it. Most subs will melt when this approach is used, and it helps avoid arguing and resentment. Pick a punishment that's easy on you, and try it out a few times. If it's not working, try a different punishment. There should be a set protocol as to how it's done to completely distinguish it from any type of playful punishment. Also keep in mind that you'll get much better results if you're consistent with punishment. With the right approach, your sub will not only behave better, but he's going to feel more submissive and horny. And that's always a good thing.