Use an older, not so forgiving cube and practise on that for a while. Eventually you will naturally have a better turning style.
This is no longer considered good advice. More often these days people are saying "get a good cube and stick with it". The only thing an old clunky cube will do is give you "cuber's wrist". Just use a modern cube.
Depends. If your turning style has been bad since the beginning, itll take quite a while to retrain your turning style. In the meantime just try turning more accurately and use less corner cutting, grip the cube less tightly and turn lighter would help. Usually a few hours is needed to correct the problems but when you time yourself you get nervous and all the bad habits re-emerge so it takes quite a while to completely change it
Definitely. When I first switched from being a lazy-wrist-turning-cube-solver to "speed solver", I had to retrain a lot of bad habits. Malkom might be lucky that he get to almost start from scratch.
At first, doing simple flicks with just my index fingers took work. So I used to walk around doing just (U U U U)(U' U' U' U')(U2 U2) without lifting my hand off the cube. Did this until both of my index fingers were comfy flicking. I'd practice sexy move (RUR'U') over and over again. Then inverse sexy. Then back sexy. Then back inverse sexy. Then all over again for my left hand. All until I never thought of using my wrist for anything. Every trigger I could identify, every alg, I drilled... over and over and over again.
Eventually you can add lefty and righty double flicks, using thumbs, ring finger pulls, index finger pushes. You add each ingredient one at a time and practice, practice, practice. And definitely pay attention to accuracy.
Speed comes with time and a lot of work. Good turningstyle/fingertricks will not necessarily come to you fast. You have to put the work in.
The best advice I never took was to watch youtube videos of fast solvers, particularly slow walkthrough solves, and just watch how they fingertrick different cases. See if you can copy what they're doing, or at least try to incorporate some of their moves into your own algs.