Plan Your Moves
Don't waste time gathering resources you won't use. Your enemy may be quicker on his toes and come to harass you while you're still figuring out what to do. Figure out exactly which resources you'll need and concentrate on gathering them. For example, if you plan on using a lot of archers in your army, you'll need more wood and gold but less food. Sending your villagers out to gather berries might not be a good use of their time.
Accumulate Villagers/Workers
Workers are the backbone of every society. Crank them out at a steady pace until you have about forty. This should be enough to keep your economy running smoothly and give you sufficient resources to build your army and purchase upgrades. To speed up resource gathering, place your granary or lumber yard right next to the resource location.
Scout the Enemy
Always keep an eye on your enemy. Figure out which units he's producing and concentrate on creating counters. If you see him producing numerous archers, don't start pumping out a bunch of infantry---create cavalry instead (see Resources for a good chart about unit relationships).
Learn From Your Mistakes
If the enemy is consistently beating you, don't keep producing the same units and throwing them into battle. Create different units to counter the enemy forces and adapt to the current situation. After you lose a battle, consider where things went wrong and think about you could have turned the tide.
Upgrade Wisely
Upgrade your units before you upgrade the armory. Upgrading specific units boosts their attack, defense and HP. Armory upgrades, on the other hand, improve only one stat.
Interface and Hotkeys
Familiarize yourself with the AoM game interface. Learn what all the icons mean so you can react quickly without having to read tool tips. Use the mini-map to move your troops. This is much faster than scrolling to an area on the game map, selecting the location and then scrolling back to what you were doing before. Use hotkeys where applicable to select and command units. Hitting a button on the keyboard is quicker than moving your mouse to click an icon on the hotbar.