It's very simple...yet hard to keep doing, although it does work most of the time. Make matches from the top 3 rows. Just remember that matching the gems below the top 3 can mess up future moves that can help you later just in case your in trouble. Another way is, you know
those power gems and hyper gems, DON'T use those immedeitally after you get them, or when the game tells you to (unless both you and the game knows that's the only move available), save those and use them when you are in serious trouble, like earlier, or a power gem could match no matter what you do as if a cascade happened! If you had made it passed level 15, good job, if not then sorry, rookies get better the more they play!