Many women like to go for a dramatic look on the eyes or lips. I say, "go for it." However, problems can occur when you try to go for both at the same time. You don't want different parts of your face to have to compete for attention.
If you want to go for a bold eye -- maybe a smoky eye, cat eye, bright-colored eye shadow with super-long lashes -- give yourself a more natural-looking lip. This way, your eyes will pop and everyone will pay attention to them. If you want to go for a bold lip -- bright red and super glossy, perhaps -- keep your eyes simple. You can wear shadow and mascara, just don't go crazy. The attention will go straight to your lips, so make sure you apply that lipstick properly!