Paint on top of paint
There is always something that isn't quite right when you begin painting, at least for me.
The genesis of a painting, always begins with the idea that this painting is for me. Whatever happens after it is done is none of my business, at least while I am painting.
I plan very little, so it is a constant surprise while the painting is coming to an end. So, The tip it is actually that you can always paint on top of paint. So don't worry about messing up. You can always paint on top. Be free and enjoy the ride.