practice single player before going online so you're not stuck reading abilities during the game.
try not to die as it gives the other team a big advantage and pisses off your team mates
set up or join games making it clear that you're new (e.g., "noob only game") until you're more comfortable against non-AI
communicate during the game and help your team mates
gloss over the strats forum and get to know one or two demigods well (sticky post is quite helpfull)
and most importantly have fun and don't pay heed to those that rage/abuse; most people are quite nice
