Each age has certain repeated stragegies. In any case, the computer player is fairly perdictable. One method to keep the ai civ from sneak attacking is to place a moble(non UU) unit near their border and in your capitol. This seems to deter civs in the ancient age.
If you enter a war in the ancient age, take units to enter their lands and pillage iron and luxaries and the roads around his capitol while building power.
In the early midevil ages, pikemen and horse can do fine defending. the horse can retreat and act as very efficient killers.
-> wait for his units to come onto roaded sections to attack... hold your fire inexchang for keeping your horse units alive.
-> industrial era is about stacks of infantry with arty obliterating cities. Build a stack(39 units) of 20 infantry/riflemen and 19 cannon/arty. march this SOD to a near by city and level it.
Building a wall of units around your country and having a single opening where enemy units enter but cant attack a city, then wax those units with arty/cannon/cats and multiple movement units.
If you can set up the kill, having a navy with units waiting off an enemies coast can make a desive victory. Or build a navy and keep it in a neutral position. Once war break out, load up your navy and sail it to the enemies coast. Land it near his capitol and raze the capitol. If you want to truely hurt an enemy civ, do that.
In the modern era, you have mech inf and MA. Before nukes, these units own and arty becomes off shore bombardment unit. Taking of cities can move at a very fast pace untill nukes.
If a civ builds the manhatten project, that means that they feel they have the tech lead to bomb other civs while not taking damage due to sdi. This is the time where you want to keep out of wars and build your sdi... unless you have the space program enable.
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That's a lot more fun than dancing around and firing weapon into the air.
