First, focus on the front sight. Never look at or focus on the rear sight.
I use to close the other eye when I was young, but what I did to avoid doing that when shooting was I would keep the left eye shut, line up the sights, then open my left eye and hold the gun just like I was. I would switch focus from my right eye, where the sights were aligned, to my left, where I was looking at the gun in a sort of isometric view.
Idk if others can do that, switch focus from the dominant to non dominant eye, but I can and maybe they can explain it better.
I will still on occasion, if I'm having difficulty seeing the front sight or the target, or some other issue aiming, close the left eye to help myself out in getting the proper sight picture, but once I do that, I will open the left eye again.