Summarize this article:

This helps prevent smudging and errors, as it’ll be easier to paint your non-dominant hand rather than your dominant hand. Stretch your fingers out wide to prepare you for painting, and pay extra attention to your dominant hand when painting it using your non-dominant hand. Painting your pinkie first and then moving around your fingers to your thumb will help prevent smudging.

Summary:
Paint your dominant hand first to make the process easier.