Practice. And do it with better weapons like the AK.
Literally this. Go into a deathmatch and practice. Go into a headshot only deathmatch and practice with rifles. Eventually you learn where to keep your crosshairs because you begin to anticipate where the enemies vital points are going to be. You peak around corners preaimed at the headshot level, and with precision you pop their head off.
After that playing competitive helps with the game sense and the call outs. It takes time, but you get better. Don't beat yourself up if you don't rank up, or you derank. You're playing to get better, and rank doesn't necessarily reflect playing skill, at least not in the lower ranks.