Age of Empires -- Cavalry and Castles

1. Advance twice to medieval age with speed. Don't bother "building up" units until then. Make what you can, but don't let it get in the way of advancement.

2. Once you're at Medieval, the fun starts. Set up 2-3 castles at vulnerable entrances to your base (total), or in a rough perimeter if there's no specific entrance that the enemy may choose. Don't overdo it. If you have a zealous adversary, 4 maximum. It will eat up your stone.

3. On a similar note, try to engage the enemy on your own ground, in the beginning. Why? Because that's where those awesome castles are, silly.

4. Upgrade them through the University. Murder Hole is a good first start, so there's no way for the enemy to rush them in immunity.

5. Unit production. Go easy on those that require gold & stone, and since they require gold and stone, keep them in the back to be your defensive forces. This is a defense-oriented tactic. For offensive attacks, I would start off with the weak-but-numerous skirmishers (elite skirmishers by now, I hope), and many basic cavalry units. Why? Because they can rush past powerful ranged attacks quickly and even more importantly, only take food to make. Farms make food renewable, which makes cavalry renewable. By contrast, there is only so much stone and gold, and less than that available to you safely.

6. Choke points. If available, obviously guard them well. With a castle, perhaps.

Offensive

1. A full queue of cavalry and a full queue of elite skirmishers to take on their main attackers. Perhaps some heavier units to supplement them if you feel arrogant, but remember, cavalry are renewable indefinitely via farms; and wood-based units nearly so due to an overabundance of timber. However, stone-and-gold-based units are far more precious.

2. The key part - after you've overwhelmed their main attack, and are near their base, get another full queue of cavalry and elite skirmishers (arbalests and knights help, as do long-swordsmen), take about 10 of your builders (of which you should have plenty farming by now, and while your forces battle the bad guys, simultaneously, and very close to, build a castle. With at least ten builders and an upgrade for speedier construction from University, this shouldn't take long. Unless you are demolished at the start, you should have a standing castle. Keep your residual forces behind/near it, and bring them out for surgical strikes on aggravating heavy units if it seems the castle is taking quite a few hits. Don't even bother with lighter units, castle takes care of them. By now, if you haven't, upgrade all you can on the University and unit upgrades (regarding additional armor & range & weapons).

3. As soon as you have your "offensive castle" up and running, make 3-4 (but not more, redundancy) catapults. Stay your guard and don't advance further until you do. Make more cavalry and elite skirmishers at the home base and bring them up to your castle, but don't attack. Once you have your catapults, deploy them in range of the nearest target. Let loose. Keep this up, advancing your catapults once they've destroyed everything in range. As you do so, bring up your cavalry & ranged forces with them for protection, but be careful not to let them be distracted and trapped by the enemy.

4. At a certain point, you should be near the enemy's main base. If you've replenished your cavalry, break an opening into their base via catapults, and if there are no guarded castles nearby (which will eat up your forces), flood the enemy. As you do so, advance your catapults to within the melee, set them up, and aim them at any nearby defenses (towers, castles). Also, simultaneously, bring forth those 10 or so builders and in all the carnage, have them build another castle right in the heart of the enemy's land. You should have sufficient forces to keep the enemy distracted and those 10 builders protected. Aim catapults at counter-attackers (enemy catapults, castles, towers) moreso than at mundane buildings like houses, town centers and "research" buildings such as monasteries. If you have any remaining forces in your home base (EXCEPT the heavy defense units that are heavy on gold-stone supplies), bring them in to continue your rampage through enemy territory. With your castle in place shooting at whatever's available, you should command a good portion of the enemy's land. Exhaust your (cavalry/skirmisher) forces on the enemy, unless they're being eaten up by enemy defenses for little reason. If so, advance catapults, keeping your forces nearby only as defensive measures, and throw stones at said counter-offensive measures, with forces keeping the catapults healthy.

5. Keep this up until you lay claim to large swaths of land where your enemy once was. Don't forget food upgrades, and lots of food (and therefor cavalry) production as the staple fighting unit. Winning should be a breeze by now.