I personally think a punishment should be related to the crime. It should not only be a consequence, it should correct the behavior. There's not one punishment that will be effective for everything, or every submissive. Each person is going to have their own likes, dislikes, limits. Pain isn't always effective. And you have to ask why a punishment was needed, if it was purposely done to get a result.
If someone gets mouthy or bratty, if they like pain, a spanking isn't the way to punishment them. Speech restriction, lines, mouth soaping, etc might be more effective. Also, if they are doing it in order to receive a punishment/activity/attention, maybe the lesson should be to ask for what they need and they DON'T get the intended consequence. These things are going to be far more effective in preventing future poor behavior.
If someone cums or masturbates without permission, maybe an uncomfortable lube, denial, forced orgasm/post orgasm torture, ruined orgasms, chastity, etc. as a punishment. Relate it to the crime so it sticks in their mind. But again, everyone is going to have their own version of "punishment". Some hate toothpaste, some love it. Denial or chastity is torture for some, others it doesn't bother.
For some, the worst punishment they can get is a lecture, knowing they let their dom down or disappointed them in some way.
You can get ideas from anywhere, it's better to just be creative. No one knows your sub or what will be a punishment to them better than you. Be creative and be fair.