Alrite,
I tried to remember this as best as I could,
I got a strategy that usually works in Warcraft, the RTS, not the MMORPG, against the AI, even on the hardest difficulty.
First, select human, hence the title.
Second, you have to know where the enemy is, I can't help here. Sorry.
Third, select your workers/peasants.
Fourth/Then, Call them to Arms, turn them into Militia. This grants them a speed bonus.
Then, charge them all towards the enemy base.
Then, have them all build towers and upgrade them to arrows.

I apologize if this isn't the 'tutorial' that's generally expected.
I didn't know if this should or shouldn't have gone in the 'Walkthroughs' thread instead.