Using the right kind and size of brush is important when doing your eye makeup.
For a dark and intense eye color, the smaller, the better.
A small pencil brush or a modestly sized tapered blending brush (see photos below)
is perfect for application and blending in the eye crease area.
Anything bigger or fluffier will just diffuse and scatter the eye shadow.
|MAC 222 Tapered Blending Brush|
|Sigma E45 Small Tapered Blending Brush|
Another thing to remember is to start with a light application.
It is easier to make your eye makeup darker than make it lighter.