Put a little concealer under the eyes - Make-Up Guide Tutorial

SAED Make-Up Guide Training - Put a little concealer under the eyes

Use a small pointed brush to dot a bit where under-eye circles are darkest, usually at the inner and outer corners of the eye.
Add a speck to other blemishes that aren't covered by the foundation and blend into the skin.
There's a little controversy about whether a concealer should be the same shade as your skin or ever-so-slightly lighter; however, it should never be lighter than one shade away from your natural tone.
Look for something as close as you can find to your skin tone and err on the lighter side if need be.