There are a lot of things in a poker game that need to be considered before thinking about the hand you have; and that at times need to be considered in a very serious way.  Your position is one of those things, and it's probably the most critical thing affecting how you should value your hand.  Position should be thought through at every betting decision before you think of anything else.

When examining position, it's common to think in terms of your place in the betting order.  Are you first?  Last?  That's the common way of thinking about it, but it's not really the right way to think of it.  What matters isn't so much where you are in the lineup, it's where everybody else is that

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By itself, being first doesn't have a lot of meaning.  Being in a position of acting in front of 9 other players does have a lot of meaning.  It's how many players who are left behind you that's the key variable.  Being first with four players behind you doesn't mean nearly the same thing as being first with nine players behind you.

Position matters even when considering how action that's taken place in front of you affects you.  Again, not just your position, but their position also.

Depending on the exact circumstances, players who have already acted might even have position behind you on the current betting round.  What I just said is that players in front of you might actually be behind you.  Think about that a minute.  It might not be as contradictory as it seems at first read.

If you're at a table with 10 players and one player has limped in pre-flop, you're next and you raise, then you effectively have a full complement of 9 players behind you.  Because of your raise the player who had limped in front of you now is behind you with respect to his reaction to your raise.  If you had just limped behind the initial limper you'd only have 8 players still to act behind you.  Your own action choices, and the choices of other players, can change your position.  Position isn't a static property, it's dynamic.

Also, it's not just current position that matters: It's also important to project your position for future rounds while considering the current and future position of other active players.  Even if you aren't in a bad situation now, will you be in a bad situation on later betting rounds?  For example, the big blind before the flop has advantageous position -- you're last if no one has raised -- but you'll be in a bad position most of the time on future betting rounds, probably having to act first.

When you're first to act the primary concern you have is that if you bet you might get raised.  If you have a very strong hand you might welcome the prospect of a raise, but even then it's a possible result that can't

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In later position you're often better off because you already know what other players have done. If someone has raised you can reevaluate your hand accordingly. But even then, there is a possibility of a re-raise that needs to be considered.

If you're on the button and everyone in front of you has folded you might want to raise with a 7h8h to try to steal the blinds.  But you probably want to fold the same hand from the same position if a player in front of you has raised.  And you might call with the same hand and same position if someone has raised but another player has called.

In the first case the chances the blinds will fold without a fight are great enough to overcome any weakness in the hand.  In the second case you're almost surely behind and don't want to go heads up, even with position.  But in the last case you're getting odds on a call.  Combined with position might make it worth taking a gamble.

Position isn't just some simplistic “Who's on first?” question.  It's a question with some depth and complexity to it.  Position is less about your physical spot at the table than it is about your temporal spot in the flow of the action.  It's the action, the projection of what's going to happen next, that matters.

Notice that I haven't really said much about your hand.  That's not to imply that your hand isn't an important factor in your playing decisions.  But the action and where you fit in the events making up the action is the context that your hand needs to be placed in.