One of the most difficult to master makeup tricks is applying black eyeliner (especially the liquid kinds.)
But the results are extraordinary and really define the eye.
Just see how great Rachel Zoe and Ashley Tisdale look with their heavily lined eyes.
Although you may not want to go this heavy on the eyeliner over 40, a cat's eye or winged look on the top lid especially will do wonders to give you a dramatic look.
One approach is to use a brush with powder to line the eyes, then follow it with a liquid liner. Lancome Studio shows how to do that in this video on makeup tricks.
Another method to appying black eyeliner is to use a makeup pen and create a winged-out effect. See how a professional makeup artist creates this look for Lancome.
And for a major cat's eye look, see how to use a brush and gel eyeliner to create a very dramatic black eyeliner look.