There’s a lot of science behind reflections. However, here’s a quick tip. As a surface becomes tangent to the viewer’s eye angle, the surface becomes more reflective. This is true for both matte and reflective surfaces. You can test this yourself by looking at your studio table. If you stare straight down, the surface is most likely semi-matte. Now lower your eye until you’re parallel to the surface. You should see the table become a lot more reflective. I mirror check the completed piece one last time, to ensure that I’m happy with the composition. I also use a bit of Color Balance to adjust and make the overall palette uniform. And then I call the painting finished!