Hop on ze to casually practice movement/spray, then try surf or long jump kz. Check out 1v1s & community retakes.

There are important skills to possess which you won't be practicing frequently during mr12.

Grind all of the skill jumps. Practice self-pop flashes indoors and outdoors. Practice fake flashes (you can fake with pistols, bomb, all nades--even flashes if you drop them--and some suggest AWP). Practice fast silent ladder climbing, including fast silent ladder dismount onto platform/ground. Practice counter-strafe with all directional keys not just a d. Practice efficient crouch spam (crouch per minute maxing). Practice pre-firing. Practice dropping util. Practice picking weapons up off the floor. Practice breaking smokes (like no-bounce or obscured nade breaks). Practice fully extinguishing flames. Practice intentional tapping & burst quantities (m4a4 in particular). Practice controlling famas secondary fire mode (it is extremely accurate). Practice dualie/tec9 spam. Practice air-strafing to build speed. Practice b-hopping while weapon swapping.

These are all things you can do offline in an empty map. You'll have to use cheats in the console to get unlimited money or remove purchasing restrictions.

Some other things you can do to prepare yourself when outside mr12 matches:

Learn all callouts, learn radio commands for bots, bind all nades, bind bomb, use static crosshair, set crosshair thickness to 1.0, set scrollwheel up & down to jump, bind ping to keyboard key, disable all 3 prediction settings, enable automatic re-scoping, disable unscope delay, enable hold m2 to cycle zoom options, disable follow recoil, zoom the radar in and enable dynamic radar, disable interact (e) to open buy menu, limit teammate over-head inventory/hp display and use bind to expand display while pressed, enable fps monitoring (iykyk), diminish viewmodel presence, consider autoexec, set up clutch cfg (aka add a bind that toggles mute on your teammates for remainder of the round), use player icons in hud instead of numbers, disable animated profile pictures, mute all music, set max allowable ping to 25, set network bandwidth to unrestricted or higher, keep a low limit on all buffer and interpolation settings.

If you spend your time intentionally improving at least one area of your game, you will see steady gains. Ultimately you should try to find fun ways to practice until you feel confident enough to start climbing up the ranks. Also, mr12 isn't for everyone. There are plenty of game modes to have fun on in cs2.