You can get free coins and gems from the game by viewing the official Hungry Shark plush toy and watching the trailers.
Make the Most of Gold Rush
When you score points, that will go toward filling up the Gold Rush bar. Once the bar fills, you'll enter Gold Rush mode, which spawns a bunch of extra fish and also fills your health. You also will be invincible while the effect lasts, and you can earn points by running into objects that would otherwise do you harm. The exact duration of that effect depends on the variety of shark you are using, and also any accessories equipped. When you are in Gold Rush mode, make sure that you move around quickly and eat everything in sight, while avoiding dead ends and long tunnels where you won't have much opportunity to eat a lot before the effect fades.
Unlimited daily bonus
To do this cheat and to get unlimited daily bonus is very easy but quite painfull. Step 1.. Get your first daily bonus. Step 2.. Leave game and double tap home button(iPhone) and stop game running in background. Step 3.. Change date and time settings to one day ahead. Step 4. Play Hungry shark Evolution again and get daily bonus. Step 5.. Rinse and repeat.