There's a wonderful kind of warm-up painting called "the 5 minute study", or sometimes "the 10 minute study", or the 2 minute study', depending on how strict your teacher is. However many minutes are allowed, the idea is to make the painting so quick you don't have time to paint in any detail.
I like it because it reveals how good we already are at zeroing in on the essential information and letting go of the optional.
So, dig out the timer from the potholder drawer, set it for a few minutes and paint! You can work in monochrome, or full palette. No need to let the study dry between layers. Squint!