Firstly, this varies so much between different species that you could almost ask a separate question for each one (for instance, most cacti like abnormally tiny pots, while most vegetables like huge pots) but there are some good 'rules of thumb' you might like to know.
First, pots generally come in sizes, and you generally want to go one size up when repotting a pot-bound plant. Don't go by the size of the top, go by the roots. They shouldn't be circling the pot inside. If you see more roots than soil, definitely use a bigger pot next time. Otherwise, just trim the roots a little, and repot in the same container.
Don't put a houseplant into a pot which is far too big. This can cause rot, and/or kill the plant. Use a pot the next size up, or if you don't have it, something only a little (like 2" diameter) bigger. You generally only have to repot once a year. On round bushy plants, the pot is often half the diameter of the branches. It varies.
On most plants, I will slice a thin layer from the edge of the rootball before planting in the new pot. This takes off the unhealthy, circling roots.