There has been a lot of good advice so far. All I want to add is this: if you have a chance for a big card that you really want, get it. it may set your collecting back for a few months or more, but that big card will be the centerpiece of your collection. And you can pick up the commons anytime.
And those big cards are the ones that appreciate in value the most.
Good luck, and if you have specific questions, just ask.
