Strategy? Depends on your team.
in aoe2 + exp, against AI
-The big winner is usually cavalry (paladins preferably). In big enough number -nothing- can stop them (top anti-cavalry units cant even slow them down), just getting 40 of them is usually enough to crush a whole lot of things.
-Longbows (massive range)
-teutonic knights (walking tanks, slow, but its like trying to stop a mountain)
-Mongol rams full of infantry (its basically a supersonic APC) and mangudai rule at hit n'run tactic.
-bring a few trebuchet to take down castles quickly. 4-6 is usually more than enough.
-Abuse walls to control AI movements
-control the sea when possible, pattrol all borders, protect all chokepoints. If you control the sea in island maps you win.
-Abuse trade. (better with spanish) = unlimited gold. DO NOT destroy ennemy docks and markets if you can help it.
-Abuse cannon ships with spanish (they are very powerfull)
-Fill transports with filled rams, then unload and attack. Bring lots of cavalry. As rams are destroyed.. more of your guys rush out.
oh, and get lots of villagers for all ressources. I like using fishing boats for food, just build fish "cage" in a corner and enjoy pretty much an unlimited food suply.