@yahleel All of those and more.
Personally I view easier variations as a base - you have to be able to do more reps and more sets of easier variation than what your goal is.
The negatives for me are a bit problematic. I wouldn't use them as a base, more like an accessory. And only do them SLOW and CONTROLLED. Hell, Isometric holds for ~5-10 sec at each angle is imho very nice builder for given exercise if you have problematic spots.
Smaller sets is actually one of the ways I manage to deal with progressions that are too big of a jump. What I actually do is something i call "Half the reps, twice the sets" meaning if my goal is 3x20 and it's HARD to do, I start of with 6x10 - it's same volume with less of an endurance component. And then I slowly increase the reps and lower the sets till hitting the goal of 3x20.
Rest is good and important, however I'm the kind of person who has not a lot of time, especially in bulk (meaning while normally during the day I can have easily 2-3 hours free, I actually get at most 1h free straight). That's why I love supersets! I do one exercise then "rest" while doing exercise for different muscle group.
Additional things to work on is recovery, accessory exercises (eg banded lat pulldowns), recovery, work on ROM, recovery, more endurance on easier variations (like jacknife pullups), recovery...
// EDIT:
There's another method that's mental but works: work to failure, then do a micro-rest that allows you to do a rep or two. Repeat until you reach double the reps you did to failure. So if you can do 8 reps max, you'd do 8 reps and then do short rest and force 1 rep till reaching 16 reps total. However this requires more rest days, but on the flip side it does build strength quite fast. It's not a nice method and I used it couple times when grinding on reps. It was effective for me, but I wouldn't recommend it.