Ehh, it depends. Since you're getting started, yeah. Closing one eye'll make it easier to aim because you don't have to wait for both your eyes to focus on the target.

[ Hank demonstrates by closing an eye and firing off a shot. He nails it, a bullseye because he really is a great shot. ]

Cops like me'll wanna practice shooting with our eyes open, though. Especially if it's our service pistol. [ He fires with both eyes open. This one misses, but only by a few inches from his first shot. ] Yeah, since I ain't used to this gun, it'll take practice to get it just right. So closing your eye helps with precision, but it won't work too well if you're facing down a perp.