1. Using a large hard edge brush, make a circle with your base color.
2. Changing the brush mode to "Overlay" and using a medium sized, soft-edged brush at low opacity. Switching colors from base color to a cooler darker color, paint a core shadow.
3. Now change your color to a color that is warmer and lighter than your base color. Paint a highlight and bounce or rim light of the object.
4. Switch to normal brush mode. Changing brush to a hard-edge and also changing the size to something much smaller and bumping up the opacity; paint your specular highlight. Also, switching to background layer and using a darker cooler color, paint your drop shadow.