Start of Game:

Have 2 Villagers create multiple houses as quickly as possible using the shift key..
Create 15 Villagers at your Town Center -- Hotkey Town Center to Group 1 (Ctrl+0).. keep building peasants... the more the better
Have your scout either protect your base or scout out the enemy hideout

Have your villagers create 4 barracks / 4 archery ranges / 4 stables.. Hot Key to Group 1 / 2 / 3

Create multiple town centers.. 2-3 town centers for gold.. 1 for stone and 1 for lumber
you can easily get wood / gold and stone.. concentrate all your efforts into military early game to defeat the enemy before you start needing food..

start building farms when your at the halfway mark..

Create units based on what the enemy is creating.. keep creating units.. dont stop
make sure you use hotkeys to create the units then gather the units in 1 location by setting the gather point

use the keys a/s/d/f/h to build your units.. DO NOT MOUSE CLICK
use s to change your units into defensive mode when needed

Halbardiers are good against calvary
Champions are good against halbardiers, huskarls or buildings
Calvary is good against archery or ranged units / siege weapons - onagers/ scorpions/ rams / trebs
Calvary archers are good against infantry
Arbalests are good against infantry
Elite Skirmichers are good against archery ranged units
Onagers / Scorpions are good against infantry but weak against paladins.. you may also use bombard cannons to destroy these siege units
Camels are good against calvary

Combat - Micromanging your units..
its best to provoke the enemy to attack you while you defend your position

Example..

When creating a castle.. make trebs to attack the enemy defenses (castles / towers) and have your units in formation to defend your castle while provoking the enemy to attack by having your trebs attack their defenses..

You may want to have your units in defensive mode when protecting your castle.. You dont want your units to be chasing your enemy into a trap..

Having a scattered formation will help against fighting off enemy siege units ie. siege onagers

You will need a variety of units to fend off an attack.. make sure to exploit the enemy's weaknesses.. do not charge your paladins into camels or halbardiers unless with support with calvary archers or archery units..

Know when to run and know when to attack -- if the enemy is defending a position and has siege units behind them.. do not attack with infantry.. as the siege will demolish your troops.. instead counter their siege with longbowmen (britons) or bombard cannons.. if the siege are not protected you can always charge with your calvary to destroy the siege units..

Once you have scouted the enemy hideout you may prepare to launch an attack by building a mini base next to the enemy.. this might be a castle / siege workshops / or barracks / archery ranges / stables.. depending what is needed most.. if you see the enemy is attacking mostly with calvary then you should build either more stables to produce camels or more barracks to produce halbardiers..

As you advance into enemy territory you may want to create bombard towers or more castles to secure your territory from further attack..

Economy..

Do not forget about economy it is of utmost important for maintaining the stability of your military.. early game u should be mining gold which is very important.. either mine gold or use a market using trade carts.. if your an archery civilization you may need wood early game and if your an infantry or a civ like persians dependent upon elephants you may need lots of food to produce your units..

The more town centers the better.. each town center can produce more peasants which allows u to mine and harvest food / lumber and gold faster..

click peasant press a then a again to make a farm..