2. Eyes Open

No matter how much you are tempted to shut the eye you are working on and just your other one to guide you, try to keep both open. You would be surprised by how much difference it can make to have the use of both eyes when aiming, and when your eye is open, you are getting a much better preview of what the liner is going to look like for other people looking at you. Otherwise, it might look good with the eye closed, but out of line when the eye is open.