These are some small tips that really helped me to improve my coloring:
✅ Don't use very saturated colors, try to chose the color with more grey component, towards left on the color wheel. Otherwise the picture will end up hiper saturated.
✅ Choose a light source and try to be consistent with it
✅ Use lots of colors when shading skin, don't stick to 3 or 4 colors darker than the base. Add warm colors like yellow, pink or orange on the light side and cold colors like blue, green or purple in the shade area
✅ Play with overlay, lumi-shade, and multiply layers, adding lights and shadows, this step marks a very big difference
✅ Make some shadows with shape or sharp edges, do not blend everything
✅ Use color wheels to build your color palettes, using the complementary color is always a good choice
✅ Add texture to the skin if you can