Hi
I'll mention one recent example where I used multiple different ways to improve part of a piece. This relates to the 3rd page of Scott Joplin's The Cascades, which has a lot of running octaves in the LH and RH, and many other difficult bits. I'm learning it for ABRSM grade 8.
I had been struggling with this page for a while, so about a month ago I sat down to practice it and I spent 20 to 30 mins playing the same page over and over, hands together and separately at different speeds (slower, normal, faster), the whole page in one play, in multiple sections, switching hands between sections - i.e. starting RH for 4 bars, then LH for 4 bars - and all of these options at different speeds.
After doing this, when I went back to playing it normally, it did seem to have improved. This was confirmed when my Teacher commented on how improved that page was at my next lesson. I hadn't told her what I'd done btw.
If I'm honest I think the piece is (or was) probably a little above my skill level. The bottom line is a lot of practise and practise in a lot of different ways.
No guarantee this will work for anyone else of course, and I've no doubt others have suggested similar ideas. I haven't read the whole thread.
Cheers