I can't say this enough... Limping AA KK up front is a great play IF you are at a particularly aggressive table, or someone is consistently min raising to your left. At your average passive prima microstakes table it is only asking for trouble and making the hand harder to play post flop.
What you are looking for a situation where you will be able to re-raise over 70% of the time. My particular favorites is there is an overly aggressive button or cutoff that has some muppet tendencies, like calling all in with KQ KJ so that I can limp re-raise all in. Limp re-raise all in is a remarkable play down low up to the medium stakes, you would be surprised how often I'm called.
The way I deal with raises is lets say one or no limpers to me from early, I'm in mid, AQ AJs just became a raiseable hand. If I'm opening out side of early I'm often raising, KQ 88-JJ also falls into that category. The tighter the table the more you can raise, the looser the more you should try to take a flop and make a hand. Pay attention to who just called your raise or re-raised and make up your mind on how to act accordingly.
There are tables that I don't bother with raising AK as they are all going to call anyways. If the A hits and is shared I'm going to get to play against a dominated hand from a muppet that can't fold any A anyways. I sometimes go as far as only raising QQ and up, three raisable hands drops my raise stat way down. There are other tables that I raise 77 ATo 98o 67s as I'm more likely to be able to raise bet any flop and take down a good pot unless someone flops a monster. Use common sense and table texture to dictate whether you should be raising more or slowing down and limping more.
Worrying about the stats is silly. There are tables that if you look at the PT stat my showdown won would be 40% how ever I'm winning big on that 40% and losing little 60% of the time. Over a week if I wind up seated with the loose passives min betting and pricing me in constantly, my stats are going to degrade and "look" bad.
PT is great, but don't become too stat oriented. It is why I can't use
http://pokercharts.com for recordkeeping, it drives me nuts to see the graph, it stresses me out if i'm winning or losing, as I want to book wins more than play to win, and losing and seeing a big downward spike bothers me even more.