Position, position, position

Most players (and most writers) tend to think of position in terms of your distance (and direction) from the button.

Particularly in no-limit games, there's a lot more to it than where the button is.

Position 1.
The button matters. Having the button is having a large weapon. Being last is good. The more active hands the more valuable late position is.

Position 2.
Aggressive opponents also matter. It's usually better to be to the left of aggressive opponents, so that you know whether or not they've raised before you have to act. But hyper-aggressive opponents are usually better placed on your left - since you don't have to wait for them to act to know that they'll likely raise/bet. Acting ahead of them lets you check hands into them and trap other players between the two of you.

Position 3.
Stack size matters. You want to be to the left of big stack sizes (if you have a big or moderate stack size).

When thinking about position think in terms of the button, aggressive opponents, and big stacks.