Wave 01
Build Anti-Ninja huts on squares 1 and 2, and snipers on squares 3 and 4. At the end of the wave upgrade your Anti-Ninja on square 1.

Wave 02
At the end of the wave, upgrade your Anti-Ninja on square 2.

Wave 03
At the end of the wave, build a Business Ninja hut on square 5.

Wave 04
At the end of the wave, upgrade your Anti-Ninja on square 2.

Wave 05
You might need wind on this stage to blow any stragglers back towards your ninjas. At the end of the wave, upgrade the Anti-Ninja on square 1.

Wave 06
At the end of the wave, upgrade your snipers on squares 3 and 4.

Wave 07
At the end of the wave, upgrade your snipers on squares 3 and 4.

Wave 08
Again, you might need wind for stragglers here. At the end of the wave upgrade your Anti-Ninja on square 1.

Wave 09
If your ninjas are a bit clumsy on this wave they might let a demon or two through. If so, use your wind to blow them back towards your Anti-Ninjas (your Business Ninjas are not strong enough to hurt them).  At the end of the wave upgrade your Anti-Ninja hut on square 2.

Wave 10
At the end of the wave upgrade your Anti-Ninja huts on squares 1 and 2.

Wave 11
Use your wind if necessary. At the end of the wave upgrade your sniper on square 3.

Wave 12
At the end of the wave you have a lot to do; build a Business Ninja on square 6, sell your snipers on squares 3 and 4, build another Business Ninja on square 4, and build an Anti-Ninja hut on square 7.

Wave 13
Keep upgrading the Anti-Ninja on square 7.

Wave 14
At the end of the wave build an Anti-Ninja on square 3 and upgrade it as much as you can until the next wave begins.

Wave 15
You should be good to relax on this wave. Keep an eye on things though, incase you need Ol' Master Ninja's wind to bail you out of trouble.