Shots can be avoided, especially those from long-range troops. Enemies will telegraph when they are going to attack. Use those movements to predict their actions and react appropriately.
Increase life limit
Defeating the Skeleton King.
Movement
Do not swipe to make your character move. Instead, keep tapping to have your character to attack as well as move.
Save Me use
Use the three Save Mes that you are awarded only when absolutely needed when you get further in the game.