I'm sure you'll be a fantastic roleplayer! You generally pick things up quickly and improve over time.
The others have perfectly explained powerplaying and godmodding! If in doubt in a roleplaying fight, it's often best to insert 'attempts' or 'aims' into your posts to allow the other character with an opportunity to dodge. For example: "She lurches forwards,
attempting to barge into the wolf's side". It lets your opponent decide whether they'd like to accept the blow (especially if it's a claw to the throat- an often fatal move!). Whilst there's a chance you'll end up with someone who consistently dodges (it'll happen with or without the use of 'attempts'!), you can at least be assured that you're personally not in the wrong in that scenario.
In terms of more roleplaying "don't"s, there's also
meta-gaming, which I've found happens just as frequently! It's when OOC information is taken into roleplay, even when the character has no way in which to get ahold of that knowledge. For example, in one of my character's biographies, it's mentioned that his mate died many, many moons ago. If I had a dollar for every female who approached him and said: "Oh, you're mate's dead. Wanna be mine?", I'd be rich.
Similarly, walking up to a character you've
never encountered before and greeting them by their name is a form of metagaming. I'd be seriously creeped out if it happened to me on the streets; your character simply has no way of knowing another's name prior to an introduction!
That's-... All I can think of for now- most things have been covered (and I'm sure you know about
Mary Sues). Apologies for any rambling!