The key to eyeliner is to ensure that you achieve a healthy thickness. Smaller eyelids do best with thinner lines, while much larger eyelids have the space to handle thicker lines. Starting in the middle allows you to gauge the level of thickness. Laying the brush horizontally and flat against the base of your lash line is a great way to start. From there you can layer the eyeliner to achieve desired thickness, and then continue following the line you created by guiding the pen flat and horizontally inward all the way to where the inner rim of your eye ends. Lift the brush and follow the same exercise starting from the middle and going to the edge of your eye. Please note the thickest point of your liner should be from the middle towards the end. As you move inward your line should gradually get thinner.