Complete the achievements listed on the side bar. Each achievement has three tiers. The more tiers you complete for the same achievement, the more gems you will earn starting with 10, then 20, and ending at 30. Build a fountain, a decoration-type building that produces a gem every ten hours. Remember to collect them when they become available. Other gem producing buildings will become available as you progress. You will be awarded gems each time you level up. Consider fighting opponents under the hard difficulty setting. The stronger your opponent's base, the more experience you will be given after victory.