Here is a trick so you don’t waste paint: Do a small study first. This paining above is slightly bigger than life size. You can see how small the study is below.
If you do a small study, you can determine what colors you are going to use, what parts should be in shadow and what should be in light. It basically helps you plan and helps you to encounter your painting problems that you are going to face on a smaller scale. This will save you time and materials.
Doing a small study can help your bigger painting succeed without wasting a lot paint.