Don't build too many buildings; a monument and a library (later +gold buildings with no maintenance and merchant slots) are usually sufficient, although you may want to specialize more in better cities. Use specialists to control population when necessary. Presumably building maintenance is the major gold drain, because even poorly placed cities will turn a profit very quickly with just a couple of buildings in them.
More development isn't necessarily a good thing in Civ V. You don't need opera houses everywhere.
