When you finish a run, you have the option to tap and view a video ad. Your reward if you do so is twenty gems. These can also be earned in the levels themselves, and are good toward in-game purchases, but the videos are a faster way. Keep in mind that if you are playing the game in airplane mode, you won't have the option of watching ads in exchange for gems.
No Ads
You can purchase a micro-transaction to eliminate the ads and just enjoy the game. If you don't have money, though, there's another way to accomplish the same thing: switch your game to airplane mode. That way, you can continue your adventure without constantly seeing ads.
Timing Jumps
As you advance, you'll come across a lot of gaps that seem virtually impossible to clear. You're likely just jumping too early, though. The trick is to run until you're at the very edge, so that your character drops very slightly. That's when you should tap the screen to jump. If you try to jump sooner than that, you won't clear some of the wide gaps.