I have a very limited imagination when it comes to video game playing, so my only strategy, no matter what race, is to build up my defenses as much as possible (guard towers, etc.), while creating as many units as possible, and uprgrading. Once I finish building an army, I send it to attack the enemy. If I fail, I start the whole process over again.
I recently tried a new strategy, however. I was playing as orcs, and I built up my defenses and army. Once I did that, I had one of my heroes sneak into the enemy base while most of their unit's were off killing neutrals. My hero used an item to build a town hall right next to my enemie's base, and then my hero back at my base used a Scroll of Town Portal to transport all of my unit's right into the enemy base! The enemy units, apparently out of Scroll's of Town Portals, had to run all the way back. By then, most of their buildings were up in flames! :yay:
This strategy is a lot easier against AI then real players, if you haven't already guessed.