I would suggest avoiding squinting or closing your unused eye (in pistol, at least). It leads to sympathetic pupil dilation in your dominant eye (not to mention the distraction of having to do it). Sympathetic pupil dilation is when Eye A doesn't get enough light because you're squinting or covering it, causing the pupil of Eye B to dilate even though it's in full light. This causes a loss of visual acuity in your dominant eye due to the over-dilated pupil.

I usually just turn my head slightly and "occlude" my view of the pistol using the bridge of my nose (one-handed, 90-degree stance). You can accomplish the same thing if you're cross-eye-dominant by using a 45-degree stance.

If you actively occlude (using a blinder), use one that's white or frosted-over, rather than a black one, to avoid sympathetic pupil dilation. Scotch tape across the lens of your shooting glasses (presuming you use cheapos like most folks) works great.

Canting the pistol is also common in one-handed shooting, but not because of eyesight. Most folks, when they naturally raise their arm, end up with their fist canted 15-30 degrees to the inside. That's just the way our bodies work. If you've ever heard the advice that a pistol should be held like you're throwing a punch, rather than grabbing a throat, this is why. Turning the gun so that it's level results in a bit of a strain in the muscles of the arm. A strained, stretched muscle or tendon is bad news for precision shooting.

The tricky part is accounting for this when zeroing offhand.