No secret, only 4 stages of work:
1) make a neat line art (I usually use thin lines and a dense brush)
2) choose on a basic color (I try to pick up calmer colors, not too colorful or dark. to the extent possible, of course)
3) add a shadow (I try to use not too gray shadows, so that the base color was not "dirty", remained saturated/bright. It seems to me that the soft shading adds volume. Shading is my favorite stage :D)
4) add lighting and glare (glare make the drawing more glossy)