These are some of the typical strategies I use when I approach a level. Feel free to comment and let me know what some of the strategies are that you use!

• If I’m going to be building a big maze, I build it completely with lvl 1 towers, then once it’s complete I begin upgrading the necessary items.
• A great way to bottleneck the creeps is to have missile towers on both sides, and a row of shock towers behind your missile towers. It’s a little hard to get started with that, but once you get both missile and shock towers to lvl 4 it really starts to do the damage. It’s even better if you can get the creeps to come back and go through the gauntlet again (just to the side of the original path), see that strategy here.
• If you’ve got some long straight paths, place 3 laser towers at the end and at the beginning of the path. Also make sure to lock them in place.
• Thumper towers go great at the end of a path where the creeps wrap all the way around it 180 degrees.
• If you want to go for a high score, you just need to start building at the finish spot. I think people cheat to get high scores though… Some of the scores are absolutely outrageous.
• The timing at which you upgrade towers can be crucial. Upgrade towers when there are no creeps for them to shoot at.

Post your strategies!