Lay in the flats for the environment
As part of my regular painting process I use a Hard Round brush set at 100 per cent Opacity to block my flat colours in. This makes it straightforward to select and delete certain areas in the painting later on, using the Lasso tool. You could also use the Magnetic Lasso Tool for selection purposes. It’s not as precise, but it’s much quicker. Depends if you’re in a hurry or not! The Eraser tool is ideal for cleaning up smaller, fiddly areas.