My strategy for playing at emperor level on a large map is as follow:
Select the right civilisation. The French kick ass. Cultural giants e.g. the Indians are nice though lack industry and commerce. Remember money is everything in the end.
Forget about culture. It’s no good if you got no more cities!
Never build more than 2 regular units. Two to start off and then a barracks. Playing at Emperor and Deity level barbarians is strong. You don’t get any attack bonuses so the hit point helps.
Research order is important. Ceremonial Burial, Writing and the Literature. You can buy Pottery and Bronze Working for about 30 gold apiece. A bargain.
Only early wonder is the Great Library. Build this in your second city. You will start with the Pyramids switch to a Palace and if you are lucky change it to the GL as you get to Literacy.
The early expansion strategy doesn’t work at high levels. At Deity and Emperor level you don’t have a chance. Get 8 to 10 cities. Build cities on water all around your capital. Try not to overlap the first circle of cities nor miss out on any area. These cities are the heart of your empire and should be well planned. Two fast producing cities (With strategic resources) will build granaries and pump out settlers. The rest get barracks and build at least 2 spearmen, an archer is possible and then cultural thingy's. Temple and library.
The wheel tends to come cheaply as well later. (30-60 gold)
You normally have either horses of iron near you. Try to get horses. They are upgradeble to knights and the cavalry unlike the swordsmen, which basically is obsolete within a few years. If you don’t have horses, build large quantity of warriors. Veteran ones. Once you obtain iron working you will upgrade to swordsmen and take the horses.
Remember that once you obtain literacy no more science research until the Great library is obsolete. If you are lucky enough to have horses you will build large quantities. The upgrade to Knights is about 80 gold each.
If you obtain chivalry for the Great Library upgrade and attack. Do not wait, as you need to take advantage immediately. When you attack take the militaristic civilisations first. My favourites are the Germans, and then Britons and then the Russians. No cultural bias but being the French these is my neighbours.
Attack once you have about 10 knights. Go for mobilisation and keep on get out spearmen/pikemen and more knights. Forget about wonders at this stage. You will take them anyway.
If you don’t get chivalry, go for it with quick research.