What make a eye makeup a success is a good eyeshadow primer and a good set of brushes! There are 4 main brushes that you should have in your make up drawer.
1- A flat stiff brush, this brush is used to apply your "main" color over your primer, it need to be stiff so it pick a good amount of color to be applied on your lid.
2- A stiff domed brush. This can also be used to pack colors on your lid since it is also stiff. This brush is mostly good used to create a smokey look, for feathering in darker colors, for applying color on the crease and blending.
3- A smaller, stiff brush. This one is used to apply color right under your lower lashes and outer corner to make a perfect "cat eye" look without creating a "Marker" look. It is a good brush to for a smudge application on the outer corner of the eye. It can also be used as a liner brush.
4- An angled brush. A brush design to apply eyeshadow as a liner. It can also be used to apply dark color over your liner to set the color. It can also be used to make defined line for more complicated but sophisticated form. Also good as a eyebrows brush.
I think with these brushes, you are good to create thousands of look and color combination! Just remember! Blending makes a make up look good!