If your mouth is too small, bring your lip color a little out of the corners of the mouth.
If your lips have a bluish tinge, a yellow-tinted lipstick worn under a normal color will help. Avoid Indian pinks, bluish reds and mauvy shades.
You can 'draw out' a timid underlip by applying a dark lip color on the upper lip and a paler one on the lower lip.
For a mouth that is too pouty, reverse the coloring. This time apply a pale color on the upper lip and a darker one on the lower one.
Make your lips look fuller by using a darker and richer shade in the centre and a lighter one in the corners.