Table conditions, chip count (in relation to blinds and others yet to act), the size of the pair and tournament position (early, middle, late...final table) all play a role in how you might want to play.

In the early and middle stages of a tournament, I like to see the flop as cheap as possible and try for the set. Especially with pairs < 9's -- you're almost guaranteed with these hands to see one, if not two, overcards on the flop and that leaves you in dicey territory since anyone calling the raise probably has two overcards to your pair. Better to just play on the cheap and see if you've hit the flop lottery. This also allows you to get away from the hand cheaper if someone behind you makes a massive raise. The minimum investment also makes it easy to remember no set, no bet. Tossing them in is no problem because you've put very little in the pot to begin with.

With pairs like 10's or those dreaded J's, you can raise here and feel more confident that, at most, you're going to encounter one overcard at the flop. This gives you a better opportunity to be the aggressor and bet as if the overcard is the one you were hoping would come.

The later in the tournament and the fewer people at the table, the stronger you can play pairs. In the early or mid stages though, you're just asking for trouble if you try raising something like pocket 7's -- the blinds are miniscule compared to the amount of chips in play and you can seriously wound your chances to go deep in the tournament by trying to play this sort of hand too aggressive at this stage (using your assumptions about chip stack size above).

Although I don't always abide by it, I try as a personal rule to not throw additional money in the pot if there's two cards on the board higher than my pair. If there's one overcard, you've got some room to play depending on what the overcard is and who your opponent is.