When you go to fill in, start by the nose. You will want to make vertical strokes. This follows the natural growth of hair. After about a quarter inch, you can move to more horizontal strokes. You can make a more bold look by doing harsh lines with a super defined arch, or a softer look by blending the edges. I usually use a q-tip to blend in and soften. Once you have the desired color, thickness, etc, do a once over with a brow brush. This helps lift the natural hairs that you have up, and yet again helps it look more natural. I’ve included a before and after picture to show you how much of a difference working on your brows can actually make.