For eye make-up I sample the colour of the outer edge of the iris. Then I use a hard brush to 'paint' make-up over the eye, and a thin line under the eye. Use gaussian blur to soften the make-up.
(try a few different thicknesses and blur amounts etc. until you get the hang of it)
Mask that layer, and re-paint in the colour (the blurring bleeds the colour into unwanted areas)
Clip a Hue/Sat adj layer to the make-up layer. This gives you greater colour control of the make-up colours etc....
Finally, adjust the opacity of the make-up layer to your tastes.