Which hands should I raise with again before the flop?
This is a difficult question to answer as it depends on your position, the ranges of other players on the table, your perceived aggression, pot size or timing of tournament, and many other factors. Please take the course Become a Winning Player in 30 days and you will have a better understanding even after the first 7 videos of what I am talking about.
For AA and KK, I would always suggest a re-raise if there is more than 2 players in the hand as you want to try to isolate a bit to reduce the variance of other hands beating yours. If 2 players or less, it depends on the pot size for me and if I am trying to have them both in the hand to increase the pot.
when you raise preflop. it's not just because you have a good hand. but it's also to push your opponents to fold poorer hands preflop. the hands you should bet with depends on your position at the tables it also has other factors that come into play including your betting frequency and your image at the table. here is a chart that can help identify which hands you can play with depending on your position.