Do some mock drafts before the real thing, it will help you figure out where players are being drafted. You can do them on Yahoo or ESPN, here is a link to another site that I like.
I think the biggest mistake I see rookies make is not drafting for value. For example, I have a friend that is playing for his first time this year and he told me he wanted to get Peyton Manning in the first round. Even if you are certain that Manning is going to break every QB record this season you still shouldn't take him in the first because he's not being drafted until at least the 5th or 6th round in most leagues.
Obviously there is the risk that someone jumps up ahead of you and takes that guy you love so you have to manage risk.
Another example, in 2010 I (as did many Texans fans) really thought Arian Foster was going to break out. At the time we had our draft he wasn't going until around the 8th round in most drafts but I really liked the guy and was worried one of the other Texans fans in my draft would take him before me. So I took him in the 5th round, 3 full rounds ahead of where he was going in most drafts. By the groans around the draft table I could tell it was good that I didn't wait any later.
Hope that helps and good luck.