Note that if you are going for a high score and are down to your last shot, you can lose points for not playing the 'ideal' shot. Just bear this in mind when considering how far away you are from your target score.
Level 12 is the last level and almost impossible to get past!
The game will be very stingy with giving you the right color bubble, and even then it's pretty tough. The best tactic is to hit the bubble off the right-hand wall as early as possible. You should also consider using bonuses, to slow down time or leave out a particular color.
Bear in mind that even if you are stuck on this level with just a few lives, you can replay previous levels to get higher scores and gain a better situation to take on the tricky Level 12.