A lot of players are very vague about what they want to accomplish with preflop raises.
For example if you pick up AA in early position in the early stages of a tournament, you ideally want to play the hand against one opponent. You may raise all-in, based on the assumption that there is always someone determined to play his A9 suited or better hand regardless of the price of admission.
In the middle stages of a tournament–say after the first hour–most of these players have been eliminated, so you want to raise high enough to deter most opponents, but still make the call possible for someone with a playable hand, but high enough to deter multiple callers.
If you just have a middling hand, but want to steal the blinds later in the tournament, then you definitely need to raise high enough to deter any casual caller, and the exact amount will depend on the level of the blinds and the size of the stacks at the table.
Or you may just want to get more chips into the pot, in which case you want to put in a single raise, that is easy to call. One of my favorite plays is to frequently raise if I am in the big blind and there are several limpers. This has the benefit of teaching limpers that you cannot expect to see a cheap flop with you Q8 suited on my blind. You may not always win the pot, but a few chips invested can be useful later in the tournament when the blinds are high and you really need to defend your blind to stay viable. At this stage the fewer limpers the better.
In this situation,if an Ace comes on the flop, limpers with no Ace will certainly fold, and limpers with an Ace with a poor kicker will be very wary, unless they make two pairs in which case they will probably raise the hell out of you.
In the very early rounds of a tournament, it is particularly difficult as everyone has a stack, and a raise to 6x Big Blind may get a slew of callers. However, if you have a pretty good hand preflop, you want to get a lot of chips into the pot preflop, and may only need to bet about 1/5 of the pot to make limpers who have missed the flop fold.
I really do not like to call large preflop raises unless I have AA or KK, because it is often better to fold and look for a better place to attack. If you call a raise with something like KQ off-suit, you may hit the flop, but be dominated and lose a stack of chips. Or if you miss the flop, it can be difficult to call a continuation bet unless you have straight or flush possibilities.
I always prefer to be the first raiser rather than the caller, because there is always the possibility of winning the pot preflop.
Perhaps I do not call enough. Obviously there are situations where small stacks are raising all-in preflop as a desperation measure and it can be productive to call with a decent hand if no more than 25% of your stack is at stake.
With good but vulnerable hands like QQ, JJ, TT, 99, you clearly want to raise high enough to get up against one opponent, or alternatively you may want to limp in and be prepared to call a raise, so that if you do hit a set on the flush, you should be in very good shape, especially if the flop comes with the top card just below your pair and someone believes he has top pair.
AK is a good hand to raise or reraise all-in with. I prefer to win the pot preflop, but at least if you get called you have outs. If there are two stacks all in ahead of you, it might even be a good idea to fold, depending on the stack and tournament situation, because if one of those hands also hold aces and/or kings, you may be blocked or beaten by an underpair.