Well, lets get started...
1) Slaves are one of the best non-combat units in the game. Why? They are perfect for diversions and human shields. And a torch is in hand for every one of them. You can send in a few slaves towards the enemy's huge plantation and burn every building in a matter of minutes as flames spread everywhere. And if you need a shield or a diversion, send these guys in.
2) Horse Archers. These guys only cost 5 gold more than their Arab non-horse counterparts and can SHOOT while MOVING. Have them patrol enemy castles during a raid and they can take out many troops. Also are good for distractions, like slaves.
3) Farms need to be placed together for better food generation and to allow more farm space.
4) CHURCHES ARE GREAT FOR POPULARITY.
5) Remember, it isn't about troop size, it is about troop efficiency.

I generally intersperse housing with taverns. Providing you have the extra population to sustain basic ale production (1 hops farm, 2 breweries), you can get an easy +8 popularity this way.
--- MrDOS

A few tips
1) The ai will always go right for your lord when attacking - use this to your advantage - gaps in you wall are and easy way in and will funnel the enemey - into death allies if you make them right
2) Towers and steps - build a tower early on in the game, a bit of wall and then steps to get arches up inside it. Then destroy the steps. Now the only way to get the men in the tower is with archers or destroying the whole tower - which keeps them alive a lot longer
3) Horse archers - not only are they fast, auto firing archers, but if you keep them moving they are very hard to hit (with arrows) as well - so keep them moving to dodge enemy fire whilst firing back themselves
4) Fire in your walls. If your on a hard mission remember that you can put pitch field inside your walls as well. Sure you might lose structures, but its a quick and great way to counter armoured units if they get into your base
5) Fire throwers - another must have unit, these guys are great when on the walls as they drop down their burning grenades. They are generally more effective than pitchpot carrying engineers since they don't need any manual firing control

A few hints:
- Always put down a trading post first no matter what along with the stockpile
- Buy at least 50 extra lumber to give an early boost to infrastructure
- Assassins in numbers of around 50 or more can do a sneaky rush over a wall to kill a lord or make a very nice distraction
- Macemen are surprisingly fast with plenty of armor, a deadly combo for a ground rush
- Wheat is the most effective food for space
- If there is a nearby quarry bricks can be made and sell very well leading to an excess of gold
- Arabian swordsmen and archers are fairly cheap when compared to their European counterparts