There's one for reaching a freakishly high score and one for finishing a stage with lightning speed. While the achievements are well balanced, they're also very hard. Zuma is a game that appears to be easy at first, but that takes a tremendous amount of practise to be good at.
When possible, shoot through a gap for bonus points. Try to avoid shooting the last ball, until at the very end; shooting away the last ball will bumps the line of balls forward a little. In general, try to focus as much as possible on the front.