Here is a way to try out a change to a painting that is nearing completion.
In the first photo you see the painting.
I am thinking that perhaps this painting needs another branch, but where to place it?
In the second photos you see a piece of colored paper with tape on it, and in the last two photos you see two different placements that I tried out.
Now why would I do this? Well sometimes you have a painting that has so much work in it that if you place a new element in it with paint and don't like it, you have to do quite a bit of work to take it out AND repaint what is behind.
This example is just that - an example.
I would not use a color so different from the painting, but I wanted you to clearly see what to do so I used a very different color. If I were really doing this for myself, I would use a piece of brown paper and I could tell much better how the placement would look.
This is something I developed on my own and when needed, it has been very effective.
I hope it helps you too!