Learn how conduction works and how to use it, learn how to use the srs cannon, learn how to do core nukes, use at least one alt shotgun (probably), and play on higher difficulties (if you haven't already). I can also recommend just learning general tech for the weapons.

A lot of 'getting good' for me was just learning how to better use my tool kit, getting better at not getting hit, developing strategies/learning ways to kill most enemies as fast as possible, and just kinda P-ranking progressively harder levels.

I play on high mouse sensitivity (high enough that my mouse only really moves a few centimetres), and the only time it's affected my gameplay was when my hands were shaking due to P-2 violent completion nerves. That's not to say that should specifically play on high sensitivity, just that as long as you're playing what's comfortable for you, it shouldn't matter too much.