At the beginning of your upkeep, look at the top card of your library. If it's a land card, you may put it onto the battlefield.
7/1/2013 Putting a land onto the battlefield this way doesn’t count as playing a land. You’ll still be able to play a land during one of your main phases.
7/1/2013 If the card is not a land card, or you choose not to put it onto the battlefield, it will stay on top of your library. In most cases, you’ll then draw it during your draw step.