I'd just like to post a couple of lessons from the trenches.
Don't tell him/her about your salary, don't let him/her handle it, and don't blow it all on him/her.
Don't expect him/her to be into all the same stuff you are, and don't force them.
Don't always act in his/her's best interests. There's a word for the other people in his/her life who did this, parents.
Don't be a dick. If you don't know quite what this means, you're not ready for the big world yet.
Don't commit early, but commit when you're ready. If you don't love him/her, don't say so just to get in the pants. You'll only be screwing with your own head.
Don't sleep with someone without running him/her by your friends first. They don't always have to approve, but you at least want someone else's input. You can drop her and pick up with your friends, but when you alienate your friends, you ain't got nothing left, and that's the sad, honest truth.
Don't date anyone you genuinely don't have any interest in.
You don't wanna be with Ms. Wrong when Ms. Right blunders her way past you, 'cause 99% of the time, you'll never catch up to her again.
When you go to pick him/her up, before you knock on the door, say their name to yourself three times. This way, you won't forget it at ackward moments.
This one is a little biased, and might piss some people off, but:
Don't date actresses/singers/drama queens/primadonnas/the self-absorbed/social climbers.
Girls nowadays are often more in love with the idea of being in love then being in love with you. Figure out which one it is, and act accordingly.
And, when you find that special someone, and make a life together, buy the most expensive, comfortable couch you can afford. Regardless of anything you may do right or wrong, you will wind up spending the night on it. And if you don't, something is seriously wrong.
Conflict is good. Constant battle isn't.
Cheers,
Max