Crosshair placement is something that takes time and practice to get good at. It’s a trait that usually comes with having played a lot of hours of CS:GO and watching a lot of professional matches. Have you noticed when watching a match in which the professionals play, how they’re always keeping their crosshair in the height of the head where the enemy player might be. How when they’re checking corners they’re already know where the enemy might be hiding and preaiming that spot before they even come around the corner? That’s what we’re talking about in this post. But how can I get better, you might ask. Well there’s no such guide that can teach you how to get better at checking corners, keeping your crosshair high enough when walking if an unexpected enemy rushes you, it takes practice. 

To some people it comes naturally. They might have played other First-Person Shooter (FPS) games before they started playing CS:GO, they might have even played a lot of Counter-Strike 1.6 or even Source. But then again, when they started, they were also a noob. They didn’t know how to get better, so they practiced, put in hundreds of hours into a game so they would get better at it. 
Getting better at placing your crosshair correctly can be improved faster if you practice on aim maps. There are many aim deathmatch servers where you can do that. To find them simple navigate here.

Then you will be greeted with something this window.

Click on “Change filters” and under “Map” type in “aim”. Also don’t forget to tick the boxes with “Has users playing” and “Is not password protected”. You can also sort the results by pressing on the “Latency” to find the server closest to you, meaning you won’t have high ping.
You can also play offline versus bots. There are certain maps on the workshop that have a practice mode auto loaded once you load the map. You can check them out on the workshop, most of them have “Aim training” in their name, so just search for that. One example is “Aim botz”. To download the map, simply open the one you want to play on the workshop page, then press “Subscribe”.

Keep in mind that if you’re already in game, you’re probably need to restart the game before you’re able to play the map you’ve subscribed to. So start the game and then:

After that you need to select the workshop in the upper center of the screen.

Select the map and click on “Start local server”. It will load the map and you will see many available options to customize your training to your liking.
Maps like these are also great to play on before going into competitive matches as a warmup. Many professional players also play on them to warmup before matches.
Practice makes perfect, so keep practicing. :)