I settle cities in a way they hardly overlap. Each new city should give me a new luxury or another strategic resource.
I don't spam cities, because each new city increases the cost of a SP by 15% - 10% if you have representation.
I like the Angor Wat wonder which reduces culture cost for border expansion.
I like to play "peacefully", warmongers would just spam units and conquer cities, so they don't need to settle more than say four to five cities and puppetting the rest.
If an alien city is already nearby or is put next to mine, and I can afford it I buy the important tiles, But I would never buy all the tiles. Sometimes I buy cheap tiles so that the next to claim tile is the one I really want - if the expansion will be in max 5 turns away.