Buy Turtle Power Magnets and other boosts to give yourself an edge
The store offers lots of items for sale. One of my favorite boosts is the Turtle Power Magnet which attracts all green orbs near you so you dont have to go after them. If you find yourself having a hard time making it past rooftop enemies, the laser bot will most likely be your best bet. Regardless what you choose, boosts arent terribly expensive, you can trigger them whenever youd like, and youre free to stock up on as many as youd like.
Focus on leveling up a single turtle instead of unlocking them all
Instead of unlocking all 4 turtles, a better strategy, at least in the beginning, is to concentrate on leveling up one. This way all your coins are going to giving you the maximum amount of armor and energy as fast as possible. So pick your favorite in the beginning and stick with them for a while.