Poker tip of the day: Don't look at your hole cards until you have to. I can't call this a rookie mistake, it is more of a rookie habit.
It is an important habit to kick for two reasons. One: Looking at your hole cards before the action is on you gives the other players at the table more time to read you and more time for you to give your hand away. I don't care if you think you have a great poker face, you shouldn't give away any more information then you have too. Two: Looking at your hole cards early keeps your attention away from where it is most needed--the other players. You should be watching their reactions and noting how they bet while you can, your cards are not going anywhere.
I know it is tempting to see what you have, and you may think you will need more time to decide how to play them. Show some self-control, your cards aren't going anywhere. If you need time, take it. Never rush for the table's sake, just keep in mind that the time you take can be a tell unto itself.