I want to talk about a few general things I figured out when it comes to aiming, although I'm just a silver player so please bare with me.
Firstly, software. Disable pointer precision within windows and within your mouse, if such setting exists in its program. This way your mouse movement gets translated linearly to the pointers movement, hence enabling you to aim better and create muscle memory.
Secondly, hardware. A lighter mouse is always better -less inertia, faster flicks, less physical recoil- and make sure its sensor is reputable for being a good one.
Lastly, training! You can train in the range within Valo, with Aimlab, McOsu and many more. Figure out what sensitivity is best for you and keep training!
Now when it comes to reaction time, training with the bots on Hard mode can help a lot.
Have fan playing,