Easy way to decide about adding elements to your painting
If you have a painting that's nearly completed, but you aren't sure about adding another element, such as leaves behind a flower or a tree somewhere in the composition. You want an idea of how your painting would look with the new element, but you don't want to risk ruining the painting as it is at this moment.
Try this instead:
Take a sheet of clear acetate or plastic the same size as your painting. Using markers, draw and colour your extra tree or leaves or whatever else you want to add to the painting. Then lay your plastic over your painting to see what it would look like. You can even move the acetate around to see where your tree would look the best.
You don't mess up a great painting, but you can 'see' what it looks like before painting in more details on the final painting.