That is a matter of opinion my friend. Mycareer is all that I play and I play for many hours during the week. Is it the greatest thing? No. But I get many hours of enjoyment (with a few moments of frustration sprinkled in).
Anyway, to the op, I don't think there is a guide for it, it's mainly something that you have to play and experiment with to figure out how to make it fun for you. Do you have any basketball experience? Do you watch the NBA on a regular basis?
I would say start by looking at the rosters of teams to get an idea of who you would want to play for, and who has the best teammates for the position you want to play.
Zero in on a couple of teams and try to make the squad at the tryouts. For best results try not to sim any games, as you only develop badges from games played.
Run plays unless you're a better freestyle person. Suck it up for that first season, learn how to play the game and then hopefully when you reach free agency at the end of your first year, you can go to who you want, as hopefully that team will show interest in signing you.
Ultimately just remember that it's a game and try to have as much fun as you can with it. Reading through the mycareer thread on here can help you as well.