Use referral code 8a0l for 100 extra gems. This will cause you to start off with a total of 200 gems, which is very useful to put towards early expansion of your city. Give this game a try, if you liked any of the Starcraft/Warcraft series games, you will like this one too.
Also, if you use my referral code (8a0l) when you create your account, then you will automatically become my friend. Feel free to message me with any questions you have about the game!