Keep your eyes to the right, which lets you know what type of wave is coming at the earliest possible moment and ensures that you have the most time to respond appropriately.
Don't bother paying to unlock the early characters that are available for 75 and 50 points, since you'll get them eventually anyway. Save up for those that cost 200 or more.
Characters are cosmetic, so only worry about unlocking them if you like the way they look.
Make sure to "Like" the game on Facebook for a free character.
