Watch lots of pro games and how they position themselves. CS GO on comp mode for an in experienced player is gonna be like running into a brick wall, peeps been playing this game for a long ass time. If you wanna legit get good then I'd suggest playing a shit tonne and watching a lot of youtube tutorials on smokes, aim, spray and map knowledge. A good stop would be https://www.youtube.com/user/TheWarOwl he has a lot of CS GO content and video tutorials/tips on how to play better. But all in all, it just comes down to playing a looooooooooooooooooooooooot.
I'm also gonna take this moment to flap my dick around a bit. These vids were from when I took the game seriously a few years ago and got reasonably good again. I dunno if Cobble is still played like this, but end of B Plat dominance was everything in that map. Smokes, awp, and some reactionary skills and you're good.
For T's: Never push through a smoke one by one. Go as a group and molly, frag, flash the stairs and push out together or this will happen:
For CT's: Nade the shit out of plat and shoot them bad guys.
Those rules can generally be applied to most bombsite push/hold. A single well placed smoke can prevent most rushes unless T's are yolo desperate to make a play.
And the luckiest worst ace of my amateur career: