Good news: if you are not changing colors you’ll be fine with one coat of quality paint (look up your situation below). If you try to save money on watery paint, this rule will not apply. (The watery stuff will not get you where you want to be in two coats!) Quality applicators and paint are less expensive and less frustrating than you think and are easy to clean. Here we go.
Be very careful and consider the results you will get if you use a paint and primer in one step. I have seen a lot of ads pushing this idea of one-coat painting, but that just plays to people’s idea that painting is a drag and one coat would be quick and easy. It is not messy and it is not hard to clean up.