My goal is to settle my cities as far and wide as possible in the beginning and later on fill up the space with cities when it's easier to build settlers (republic). When you have 2 cities very far apart, you can build roads relatively cheap. Here's the good part. A city acts as 1 movement point. If you are able to build long roads between your oldest cities, try settling your new cities adjacent to those roads. You can get from one city to another in just one turn. A few drawbacks: If an enemy unit is on that road, your unit goes offroad automatically (which is annoying, it should stop and let me decide the next move like it has always done). Enemies can use the highways too.