Research advancements like Iron Working, Communism, and Construction to enhance your civilization s technology. But don t get so centered on expanding your civilization that you neglect your civic duties a happy, well-fed and educated population is the key to success. If the population thrives and is happy, your civilization can churn out military units and Wonders a lot faster than if there is civil unrest. And you d better make sure your cities are well defended because nothing can screw you up faster than an unexpected attack from barbarian hordes. Settler units should always be on the move, laying down roads, irrigating the land or mining for ore.
Roads allow units to travel further during their turn and also enhance trade between cities.
Trade and commerce are especially important if you want to maintain your military and cities. The place is totally open to your own strategies. Maybe that s the aspect of Civilization that makes it so playable the player gets to do what he wants to do instead of trying to decipher what the designer had in mind. The design is so open-ended you will never have the same experience twice. It s totally up to each individual player how to proceed, but those looking for success will strike a balance between expansion and consolidating wins by improving cities.