Position is simply the single most important and valuable commodity to have at the poker table.
The button is your friend
If you're unfamiliar with the term, position simply means you are the last to act in the hand (meaning you have the dealer button, or the players acting after you have folded).
Positions on the table
The worst places, position-wise, are typically the blinds, as after the first round of betting the whole table acts after you for the rest of the hand.
Regardless of your skill level, the situation, or the hand you're playing, being in position will always give you more information in the hand than any of your opponents.
And in the world of Texas Hold'em, information is the most valuable commodity there is.
Four Biggest Reasons to Play in Position:
When it's your turn to act, you have more information than your opponents.
Position gives you "bluff equity," meaning simple, cheap and effective bluffing opportunities.
Acting last lets you make more accurate value bets.
Having last action gives you control over the final pot size.
Adapted from "PokerListings"