great strategy for early rounds. Build one, only one, tower near the anthill. Make it a double, then triple tower. When you can make it poison sprayer one then two. DO NOT buy anything else until you have a poison sprayer two. You will almost never lose a piece of cake if you do it right until later.
good tip. Freezing wind has low mana cost and good damage. If you have good will, you can spam it a lot. Also attacks like it can reach through walls to kill enemies without a fight.