Epic defense is a strategy game with medieval age theme. If you have't played it yet, you can play it here
There are many strategies with which you can win the game in each and every mode. However there are few elements that are common in all of them. You need to get first two gold for kill upgrades from upgrade screen as soon as possible. Also get first population upgrade and gate upgrade after first 4-5 waves. General strategy is to mass up archers fully, get their upgrades. Now you can focus on one unit, maybe knight or two handed swordsman and start upgrading it with time. Armor and attack, I consider most important upgrades followed by attack rate, health and range. You can win easy, normal and hard modes with that strategy. However insane mode as the name suggests is little insane but not impossible. For that you need to be very careful on choosing upgrades.

To Clear insane mode, follow the following tips:-
1) Dont hire any melee unit for first few waves
2) Mass up 5-6 archers, then buy first two gold for kill upgrade.
3) Dont buy any more archers but buy all of their upgrades. Make sure you dont lose 3 times in a row while doing that.
4) Now unlock knight and start buying knight upgrades before buying any knights.
5) After you have bought one armor, two attack and one health upgrade, buy few knights.
6) As waves keep coming, make sure you buy 3rd gold for kill upgrade and as many knight upgrades as possible fast enough.
7) Keep buying knights and keep killing units, gold will start to accumulate, with which you take your pop to max 45 pop.
8) After that upgrade knights fully and keep placing knights.
9) If you are losing a level first time then concentrate on one or two gates and guard them heavily. Mass all your knights there. The best gate to choose if you have full 15 archers is the gate at 5th tower. That gate is covered by all archers.
10) Battle No 11 and onward in insane mode will require a lot of gold to place your fully upgraded knights. Dont buy any upgrade other than those of the units you are making as you will end up wasting that gold.
If you lose in the insane mode first time, you will get to keep unlocked units, next time you try it. That ways you wont have to spend any gold on unlocking units. I hope you like the game as much as I enjoyed making it. You may leave your comments and ideas in the comment section on the game.