Every game try to get as much amulets as you can. For every amulet you get extra experience points. If you build towers - build either 3, 6 or 9 of them. If you throw gem bombs - try to throw at least 15 or 30, so you get the extra amulet. Extra amulets = extra exp, and if you get the full blue frame after completed level you can get a bonus level as well.
 "GemCraft"){kind=icon}
 "Desert Moon"){kind=icon}
 "Crunchball 3000"){kind=icon}
 "Colony"){kind=icon}