One word. Merchants.

There are a couple of Ivory and slave spots at the castle down at the bottom of the map. By the way, I changed that castle to a city in the beginning. Make sure to start your all of your merchants from a town with a merchants guild.

Also you should be Jihadding like crazy. As Eygpt, you can Jihad on turn one and I keep doing so the whole game.

Take out the Byzantine Castle on the island west of Acre. Put watch towers up to keep track of ship movements in the eastern Mediterranian.

I kept Acre, Adana,Mosul and the castle next to Cairo a castle (can't remember the name).

Any castle that you don't need to produce units ,change into a city for production. In those cities build only the necessary items for pacification of the populace,making money and build nothing else except at one or two cities that should create most of your units. Those towns should specialize.

You should try to capture as much as you can as the Mongols arrive at around turn 80 and they can cause you major problems. Take out the Turks. Those good for nothing infidels are worst than the infidels....er sorry, got carried away. But I never could make peace with them. They tended to attack me first.

Others may have better advise but this is what worked for me.