When putting on eye shadow you can try this. Apply a "base" lighter color over the entire eyelid and under the eyebrow, be careful not to let any access eyeshadow to fall on the cheeks or under the eye.
Choose a mediumly darker color and apply it to the inner third of the eyelid and "run" it to about half way to the corner of the outer eye. When applying eyeshadow to the crease of the eye, keep your eyes open and slightly tilt your head backwards. This will enable you to better see the shape you are creating and allowing the shadow to go into the crease.
Then apply the darkest color in a thin but blended fashion above the eyelash. Blend away any viewable lines in the eyeshadow.