Obviously there are no rules to what you do to a plein air painting in the studio. My plein air work is primarily practice and gathering material for larger paintings (along with photographic references). I like to keep most of these pieces to judge progress in my work over the years and as a file for painting material. The plein air process is so different from studio painting, more of a quick response instead of a planned painting so I don't want to kill that feel in the studio. But I will look at a few things once I bring the painting inside -- one is edges. I decide where I can soften or harden edges to create more depth. Another is contrast -- small, dark accents or light highlights to pop the contrast. Third would be to knock down detail if I was overly excited outside and added too much.