basic requirement for all, reasearch technologies so you have more advanced units, and in civ 4, control religions. Also build cities to block off your opponents access to natural resources, but don't overbuild, Shields are the most important production resource, but don't ignore your food, try to make sure your city is always growing.
if you want more tips, Give me a specific game, but not civ v, I haven't played that yet.
