Most important things go first. What is the most important thing to do to improve my rank? It's pretty much obvious actually when you think about it, and the answer is - Practice. Counter-Strike: Global Offensive is not a shoot-kill-win game. It's a game that requires strategies and strategic thinking before your shooting skills. You can't rush into B site and win the game, you have to think what to do when, and you can't do anything alone. You have to make others believe in your thinking, lead your teammates if you want to win the game. I have personally spent 1500 hours in this game, and I don't regret a minute of playing it.
You can practice on a lot of ways in CS:GO. One of them is deathmatch. Deathmatch is surely going to improve your shooting skills after some hours spent on it.
The other way is community-made maps, community-made maps for training. There is a lot of them actually, and all of them are aim training maps, you can't train your brain on bots(actually you can but only if you can talk with them). They are pretty easy to use. First of all, you have to find a map you want to use for training on the steam workshop page. When you find it, just press "Subscribe". Launch CS:GO, press Play and select OFFLINE WITH BOTS. On the map choosing menu select Workshop- All maps, select your map and just press START. Aim training maps usually improve your one-tap skills and your reflexes, which is very helpful in every phase of your game.
There is one more way to improve your cs:go shooting skills needed to mention, and that's CS:GO tournaments. You can always practice your shooting skills against bots, but will it be helpful as playing for money against good CS:GO players? These tournaments are usually played 1v1 on aim maps, so you'll do your best to go as far as you can in the tournament and you'll improve your shooting skills in that way.
What else is important for my rank improvement? As in every game, In Counter-Strike: Global Offensive you'll also have to show honour in your games. Don't be a toxic player, CS: GO community is already full of them and nobody needs one more. Instead of flaming your teammates for every mistake they make, try to teach them how to avoid it. If he rushed outside the site for the kill, explain to him why is that not a good thing to do and he won't do it again next time. If you start flaming him for that, he's going to rush outside the site 10 more times just to show you that he can take kills and show you that he's not that bad as you are saying. Improve your communication with other players. Don't treat them like bots, treat them like a person you would treat in a real-life, and believe me - You'll be shocked how much this is going to improve your games. If you manage to do that, even when you lose you won't be sad because you had fun with your teammates.
Now, after we have improved these things, let's talk about settings. You can't improve your skills if you are changing settings every day. Instead of that, figure out what settings work best for you and try to play always on the same ones. There are no "configs" like in CS1.6, but instead of downloading "f0rest" config, try to make your own. Find out which audio, video and control settings work well for you and play them. Instead of using your mouse sensitivity on 7.0 for your "AWP skills", lower them down, man. A lot of pro players play on 400 dpi for their mouse sensitivity and 2.0 sensitivity slider In-Game. It may feel pretty boring and ugly when you lower it down, but try to get used to it. When you get used to it, your shooting skills are going to get a lot better. In this article, I'm going to talk about one more thing important in CS, and that is definitely economy. Learn how it works. You can't rush armours and grenades every round, you won't have anything for the round after that. Win or lose, you'll get money. That's true, but learn how much you are going to get and if you win or lose and then start buying grenades and armours, pre-calculating your next-round starting money. Saving your money and trying to fight enemies with a pistol is a great thing to do in this game as you'll be able to have more than other players even if you lose some rounds in a row.
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Complete the tasks
Every game has some tasks for which you will receive Soul Gems.
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.