I find that it's helpful to be able to place the arrow point somewhere on a vertical line through the spot you want to hit, rather than a line that is offset right or left. Usually, this means that you select an anchor that puts the arrow is directly under your dominant eye, and tune the arrow from there so it hits on that vertical line through the spot (assuming you're doing all the good things recommended by Bowguy67).
The specific skill you need to develop to shoot gap is to always focus on the spot you want to hit while keeping track of the arrow point in your out of focus peripheral vision. If your focus shifts to the arrow point, you will miss, usually high in my case. This is an easy error to make, and you should keep it in mind.
Another thing I occasionally do is to get everything all lined up and then lose track of the arrow point as I concentrate of the spot I want to hit in the final moments of aiming. When I do this, the arrow point tends to drift up and I again miss high.
There are two basic gap methods: true gap where you work out measured gaps for specific distances, and “instinctive gap” where you don’t work out measured gaps, but instead just shoot arrows until you have a feeling as to where the arrow point should go. Feel free to experiment with both, if you want to.