Do you even CS GO, bro? de_train included. [SGTools]

In all seriousness.. How do you get better at anything? By practicing of course!

If you really want to "git gud" at the game, you have to play quite a lot.
Basically play every day, do some deathmatches or aim maps against bots before matches. Can't really say how much, as it varies how long it takes for a person to warm up. Learn how to tap with various weapons, and how to spray.
Preferably play with people that are on your level or slightly higher. It's hard to get better by playing against lesser opponents. Soloqueue is cancer, don't do it.
If you feel like you're strong in a certain role, concentrate on that first. Try to get really good at the aspect you're already strong at. Look at demos of pro players who play that role, and try to emulate things that they do.
It's really helpful to learn some of the most basic smokes (and other nades) for each map, so look for tutorial videos and go practice them yourself on an empty server. Your team should know the smokes as well, so you can do proper executes on bombsites.
Crosshair placement is very important. It makes fragging a lot easier when opponents are likely to just walk into your crosshairs.

Those are perhaps the best tips I can give you. Other good ones have already been mentioned.
This is more of a "do as I say" and not "do as I do" as I don't do most of these things :D.
But that's because I have a long history in the original Counter-Strike, so even tho I took like 7 years off CS, I got into CS:GO quite quickly.
I'd say I'm actually quite a crappy shooter and I basically never warm up for games and I only play a few games per week, but I've managed to do well in the game with my old knowledge and "gamesense", which you can only develop by playing more and more, so you get used to all kinds of situations.

So as a TL;DR: PLAY MOAR! :D

Thanks a bunch, especially for the links, will take a peek (hehehhee)

The owl won't teach a wolf how to bite, you know I~voI The true wisdom is knowing your limitations!

Should I make my targets ADAD or stand still and go for 100?

I would do a little bit of everything (going for headshots on standing enemies, headshots on moving, sprays on standing and sprays on moving) since you do encounter a bit of everything when in game. I would also warm up on the map before every first game of the day.

Do I "counterstrafe" with S? or do I crouch? or release W and hope for the best?

I might not be the the best person to answer that as I am an AWPer and dont tend to deal with riffles all that much, I just let go of W. I have never seen anyone stopping with crouch tho. The most important part is just that you do not shot and run.

Adding to my previous list: if you haven't nailed it down yet, practice the recoil pattern for at least the first 10ish bullets (you generally either kill them or die by the time you shot 10 bullets anyways) for the m4/AK and anything else you use a decent amount. I dont know what is your sensitivity, but I would try to keep it as low as you are comfortable with. Personally I keep mine at 400dpi and 1,49 sensitivity in game, but that is on the really really low side.

Tapping "S" while running forward will be the fastest way to stop, turn sv_showimpacts to 1 to see exactly where your bullets land (to know if you've waited enough before shooting, or cl_showpos 1 can help as well). (Video on this)