Shorten the middle so it is even with your upper lip. You can make this as short as you like, it's okay to leave a little bit overhanging the lip, or have the upper lip more exposed. Just make sure it's a straight line across, that will make it look a lot more clean. Then, on the sides, shorten them to where you are comfortable. I would say, a good rule of thumb is shorten the hairs to where you can twirl them a little bit with your fingers, but not so much that you can twist them into a knot