If you only upgrade one thing on your ak, it has to be this! - GG&G AK47 Ghost Ring Replacement Sight

I highly recommend this ghost ring replacement from G&G. I installed this on a Century Arms VSKA Trooper rifle. It drastically improves your acquisition time over the standard slit AK rear sight. In addition, it allows you to see more of your peripheral vision through the ghost ring which helps in target identification. If you can only upgrade one thing on your AK rifle, it should be this. As another reviewer mentioned, I won't even bother with putting an optic on my rifle because of how effective this ghost ring sight is.