Well, I wouldn't call myself a 'seasoned' roleplayer, but I've been around the forums a couple times.

1. Read the rules and follow them! As a beginner I had trouble with this. Trust me...just...do it.
2. Don't mess with other people's characters. They will get
really ticked off at you. And it's against the rules.
3. Avoid one-liner roleplays. Sure,they're easier, but they suck. I have never read a one-liner/nonliterate roleplay that came anywhere close to a decent plot, or nice characters.
4. A personal rule of mine is that I won't roleplay anything I wouldn't do in real life. Just a personal thing, but I thought I'd put it out there.
5. Description will boost your word count and it's awesome. Rather than "The wind blew through the trees." try "Rustling leaves sounded all around [your character] as the wind raced in the evening light."
Ok, that's my basics. For general information, the roleplay school is suuuuper inactive.