How to i get good in CS (or get the practice there for)?

Besides playing workshop aim maps and community server 1v1 arena, DM and so on; I would recommend to learn different smokes, flashes and mollys as well as solo entry routes on different maps.

These videos are pretty good imo for solo queue'ing:
https://www.youtube.com/watch?v=agWbRM-cYcQ
https://www.youtube.com/watch?v=W4TQvs1QjA8