The boost meter is located at the top right. Time boosts to get better distance and more skips, usually as soon as your fish hits the surface of the water. However you may want to use it during your final run once close to the finish line. Each yellow boost you collect will increase your overall boost bar.
Launching
Each fish as a sweet spot in the angle used to launch them. You will have to remember the optimal angle to launch a particular fish to get the best distance.
Leveling
Earn experience by completing the stage goals with the appropriate fish. You can view the stage goals by tapping the checkered flag at the bottom right. You can also improve the overall level of your fishes through collecting all the treasure chests from the level, as well as completing the achievements.