Introduction :

Doing all of this, will take some time. So try to do this when you got a few hours to improve on csgo. Most importantly try to do all of these steps and you'll see a better result.

This order will be from Most Important to least important. (My Opinion)

1. Crosshair Placement
2. Game Sense / Map Awereness
3. Flickshots
4. Spray Pattern

1. Crosshair Placement

Okay, so first of all. Find your personal Crosshair :
https://gtm.steamproxy.vip/sharedfiles/filedetails/?l=dutch&id=308490450

Then find the sensitivity that works for you. You should be able to make 1 taps, spray and flick.
https://www.youtube.com/watch?v=ct8U06Wonhk

Now, lets start with Crosshair placement. I think this is the most important factor of making 1 taps on csgo. When your placement is good, you only need to click the mouse button and you killed an enemy. That leads you to the question, how does crosshair placement work? Well TheWarOwl made a nice video about it : https://www.youtube.com/watch?v=li0qTAa6IHw

Now, the next question is : How do you practice it? Well in my opinion there are alot of ways to practice it. Many people practice it with community maps where they just 1-tap bots, by peeking around corners. Example : http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=533515529

I trained my Crosshair placement by practicing on prefire maps such as : http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=694731018
Tip : Try to make headshots only

2. Game Sense / Map Awereness (All examples are from Dust2)

I think this should be ranked 2nd, because your surround sound can give alot of information. They can tell you how close enemies are, how many enemies there are and where they are. Also Game Sense is pretty important for information you can make by sounds that you hear. Things like, how many nades are thrown? (2 nades = 2 enemies), Or what shots did you hear? And where did they come from? All of these little details are important for the outcome. Example : If you hear 1 AWP sound on A site, you probably want to smoke it off, or wait till a teammate can kill him from long.

The question is, how do you train it? Well I think it's just getting trained by playing alot. You can practice your surround sound by using this : http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=697998669

And I also liked to use this to train your actual in-game Sense : http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=703668900

But, really all of these are trained by experience.

3. Flickshots

I think this should be ranked 3rd, because Flickshots are really important, but really hard to master and train. You will need skill, a high reaction speed and alot of training. Flickshots are actually the most important factor of aiming. That's because if you can flick like a pro, you can flick from any crosshair placement in the head of the enemy. I trained my flicking by playing alot of AWP on community servers and training on maps like :
http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=368026786|
http://gtm.steamproxy.vip/sharedfiles/filedetails/?l=dutch&id=243702660

To train your reaction speed : http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=241148414

But then again, it's hard to master and you'll put alot of time in mastering it.

4. Spray Patterns

I think this should be ranked last, because you don't necessarily have to spray. The only situation I think spraying is the best option is when you hold an angle close and you hear alot of enemies rushing towards you. But, some people like to spray and sometimes it can be a good thing. Since you only need 5 bullets to hit, try not to spray more than 10-15 bullets a time. The best map to practice spraying is : http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=419404847