Dark circles look darker when liner is applied on the lower lash line. Bring concealer up to the lash line, and use only mascara on the lower lashes.
Make eyes look more intense by double lining. Use a dark shadow with a dry eyeliner brush, then repeat with a liquid liner or wet brush using a slightly thinner line. The gradation in depth from the lash line will give a dense look to the lashes. The technique can also be reversed—gel can be softened with shadow.