As much as I like the adjustable steel sights that the military has standard on M16’s/M4’s, get a cheapo holographic sight thingie. When I say “cheapo” I mean, cheapo. You should be able to find one new for like $25 US. My eyesight isn’t the greatest and my hands aren’t the steadiest and these are great for compensating for that at ranges under, like, 50 feet when trying to fire at a target unsupported. These doohickies can speed up the time it takes for you ready the rifle and find your aim, aiming when wearing glasses or goggles, sweat in your eyes, or firing from less than ideal body positions with some confidence that you can hit some part of your target.

Just for the record, those cheapo sights will not last. Not only will they break quickly, but they will not hold zero for more than a hundred rounds or so. If you really need a red dot or whatever, invest the money ASAP. Holosun and Vortex both make some affordable-ish options, and if you've got the cash, Sig and Trijicon make some bangers.