Just keep playing and concentrate on playing the actual game and collecting as many coins as possible. Before you know it, you'll have lots of coins. If you can, connect to Facebook, watch ads if they have them, complete tasks. :) good luck!
I play the popular iPhone game, Subway Surfers all the time, but I am trying to unlock some of the limited characters. I only have 50000 coins, though. Anyone have a strategy for quick star coins?