How do I get better at CS:GO?

Lots of Practice. Its cliche but its also true. Practice aim, try lower sensitivity, and take a break so often

just got to keep training deathmatchs and keep playing competitive and get scolded and learn!

Make sure you have a good PC (if you don't already), then literally just practice your aim. You'll get better in no time just by playing the game.

It's all about aim, and having positioning. Stick to strategies and make sure you have a decent enough aim to follow up with it.

Simple way to get better are lerning the maps you need to lisen to foot steps of your enemys sneak so that you dont case steps play as a team and you need to learn to shoot that means no moving and shooting

Doesn't really matter what gamemode you play. Just, the more you play the game the better.
The best way to improve a skill is to do said skill over and over again, trying to improve yourself in every way possible.
As long as you're playing the game, you can play whatever. Deathmatch is ok, but you won't have much chance practicing pistol skills against people with AKs and M4s. It's better to play Casuals or Competitives for that. The more games you play the better your rank will become if you derank, that's OK too. You'll play with people more suited for yourself then, and you'll have more fun. That's what games are all about.

if you really want to get better you'll need to do exercise like deathmatch or aimbotz

There are a lot of cards to train in workshop where you can practice or better, find a group of people for training well something like that.

Oh yes, something that I forgot to mention, there's a ton of Aim maps, and Smoke maps, and Flash maps and things of that kind that'll help you fine-tune those smaller and important skills.
If you use them correctly and practice on them often you'll be able to prefire corners and smoke things like a professional.
Once you have that down, you're going to be a really good addition to any team.

-Though I'd mention that you should only really do these kinds of things once you've at least tried to master some of the basic weapons, otherwise these would be kind of pointless.

Best thing to do is trying to get better with reaction times and aim, and you'll climb in no time.