Good roleplaying looks like this

To some extent it's subjective what constitutes good roleplaying, particularly as you get into the distinction between really good and supremely good. However, I think when it comes to the distinction between good roleplaying and not-so-good (or even bad), that can be defined clearly enough.

1. Your character's behavior always corresponds to what that kind of person would do in that kind of situation in that kind of world. Always.
   
   
2. You can play a character who is not merely a simple variant on yourself, or a simple wish-fulfillment version of yourself, without violating rule #1.
   
   
3. What you do doesn't just conform to the world, setting, theme, and tone, it also helps build it up and establish it.
   
   
4. Your actions are always done in a considerate way that enhances, or at least does not detract from, the enjoyment of the other participants, always. You manage to do that without conflicting with rule #1.

I think that pretty much covers it. If you do all of these things all the time you are probably a good roleplayer.

Amusingly, in my 25 years roleplaying, without exception, every time I've met someone who believed themselves to the best roleplayer they knew, one who would "show the rest of you how it's done", they were invariably bad roleplayers who regularly violated at least one of these rules. The best roleplayers have always been people who considered themselves about equal with most of their peers at roleplaying.