Different eye shapes can be handled differently by contouring the eyes to enhance features you want to enhance or downplay features you want to downplay.
For eyes that are wide set- have a large distance between them- you want to emphasize the inner corners of your eyes so as to not make them appear so far apart. One way to do this is to put hilighter on the inner corners of your eyes to draw attention to them. As far as eye shadow goes, you want to make it slightly darker towards the inside of your eye and lighter as it goes out, and line your eyes starting at the inside and go half way out. Apply most mascara on the inner lashes
For eyes that are very close set, you want to emphasize the outside corner of your eyes. To do this, you want to put the darker color on the outside half of your crease, and apply your lines from half way across your lid to the outside and extend slightly past the outside to create the illusion of your eyes being wider. Also, when applying your mascara, put most at the outer corners and use the brush to spread them out as wider as possible.
For small eyes, you want to focus on lighter colors to brighten your eyes and make them stand out more, and avoid darker colors as they will make them appear smaller.
The following diagram shows
more specifically how you can expertly contour your eyes based on your specific eye shape
Clinique makes wonderful eye pallets that make it very easy to find colors that complement each other and can contour your eyes. In each pallet there is two colors, the base color and the contour color. The base color is the bigger swatch.