Most anchor on the corner of the mouth, Others their cannine tooth, others their cheekbone. It is really up to you. You should use the anchor that feels most natural and comfortable to you. Once you have established a solid anchor, you then can focus on accuracy. Me... I have a high anchor, I actually use a double anchor. First anchor middle finger to the crease of my nose, second anchor is my drawing hand thumb to the temple. This puts the arrow directly under my eye. I shoot split finger... never could get use to 3 under.
To find your natural anchor stand with both arms extended out at the shoulders, shoulders aligned parallel to a target (imaginery or real) bow arm should be pointed towards the target, close your eyes, now take your drawing arm / hand and keeping the elbow extended back in place, bring the drawing handing back to your face, wherever your middle (anchor) finger is placed is where your natural anchor is.
Good luck.