That may sound a bit off-topic, but on other games I've monitored some players to help them fix some of their flaws and the most effective way I've seen to help improve their aim was tuning their sensitivity down.

When I started playing FPS on PC, I was playing with a sensitivity that'd equal something like 2/3cm for a 360° turn (aka moving your cursor to the right (or left, whatever) until you make a complete turn). This is extremely high. Now I play with 41cm/360, and that's really low but I mainly use it for Counter Strike and carrying the same sensitivity along games helps with muscle memory.

Point is, you probably play with an incredibly high sensitivity and that's anchoring you to a bad aiming level. Try lowering it to something around, say, 10cm/360. The change will be abrupt but when you get used to it you will not want to go back.

Going into practice range for 10/15mn every day before playing just to shoot off some bots' heads will also help you warmup and build up your muscle memory.

Other than that, not to walk on that video's feet, try to look at your target, not your crosshair, make efforts to aim with your crosshair, not WASD (it's tempting when you could just strafe left to hit that shot, but in the long run aiming solely with your mouse will help you), and slowly incorporate strafing into the mix.