There are 169 different possible combinations for holdem preflop. Only about 10-20% of these hands are playable in a tight strategy. When 20-30% of these hands are played, the player will often be labeled loose. Over 30% usually places a player in the maniac category.
One important factor on the preflop decision, and maybe even the most important, will be position. In a 10 person ring game, the strongest position is the button. This position is named from the dealer button placed in front of the player. The button is used to specify where a dealer would be if there weren't an all-time dealer, like in a casino.
The button is the player who will be last to act on every round, except preflop. The blinds, who are the first of the early positions, are directly to the button's left, small blind then big blind. They are last to act preflop because they are forced to put money into the pot before any cards are dealt. After the blinds, the next position is first to act preflop and is thus called "under the gun" or UTG. The blinds and UTG are referred to as early positions or EP. The next four positions are called middle position or MP. The final three seats are late position or LP and are named the hijack seat, cutoff seat, and button. The position called the "hijack seat" can steal from the "cutoff" before the "cutoff" can steal from the "button". But if the hijack doesn't use his position, then the "cutoff seat" has the chance to cut the "button" off from making a play.
While the button has the best position, the blinds and UTG are in the worst positions. The blinds have an advantage, since they already paid into the pot they can see the flop for a discount or the big blind can check to see the flop in an unraised pot. Because of this fact the UTG seat usually has the easiest choice to fold unless they have a very strong hand. Without getting into too many crafty plays this is a basic introduction to some preflop thoughts on holdem.