How the FU#K do I get better at this game???

A relatively new player here, ever since FUNKE reviewed this game I was immediately hooked on. This winter sale I gave in and bought the game. I can clear levels on normal and struggle on bosses for just a few tries .

I have been slowly learning how to play and turned on aim assist, but feel stuck and unmotivated.

Any tips, tricks, videos, and controls that you guys use please help a brother out.

I want to be as flashy as possible, chaining weapons, doing combos n all.

Every video I watch is telling me some complicated mechanics that are sure to give me arthritis and i don't even know how they switch this fast.

Any tips will be appreciated, help a fellow machine on its way to hell eh?