Eye Brows The most important focus for the entire face is the brows because they frame the eyes and balance the face. The angles of the brows serve as a guide for every other angle of the face. Think of brows as comprising thirds - the inner or ascending third, the middle or arch and the outer or descending third. The ideal brow adds lift and can give the illusion of making a narrow face wider or wider face narrower.
Most of the time, the shape you were born with is the shape that works best with the eyes and face. So, let that be your guide. You may have to cleanup the brows, although be careful not to be too radical, because hairs often don't grow back. Nature designed the brow to keep foreign particles and sweat out of the eyes. They and the lashes are there to protect. Just as you may want to adjust brows that are too asymmetrical, don't fall into the trap of making them too symmetrical either. If you use stencils, the brows will look too perfect and, therefore, artificial. No one has completely matching brows.
They shouldn't be too dark or too light and NEVER one color. Most brows have thin places. Comb the brows down and color the sparse patches directly on the skin with an eye shadow. If the brow needs lengthening then extend the brow with the shadow.
Never use black. Black brows are aging and should be highlighted so they soften the face and don't take the focus away from the eyes.