In terms of pure strength training I do trills for each finger permutation on a random string. So if we assume 1 = index and 4 = pinky. I would trill with fingers 1-2, then 1-3, 1-4, 2-3, 2-4, 3-4 for a minimum of 30 seconds each (adjust according to strength and gradually buildup to 3 minutes or so). Furthermore, these trills would be nothing but hammer ons and pull offs (so no picking), and you must keep a certain dynamic. An example can found here.
In terms of accuracy as mentioned by @lilsam138 the metronome is the way to go and I think their answer explains it well enough.
In terms of increase reach this is something you acquire with time as it require you stretch it just like any other muscle. In terms of an exercise I use this one quite often. Here is a video from such said site explaining the exercise.