Best excerise I can think of is wide stretch legato stuff (legato=hammering on, pulling off). On an acoustic guitar something a bit easier is perhaps advisable try hammering on the first fret with your first finger, second with the second etc.. keep previously fretted fingers in place on the string. Do this from low string to high string. If you can do the top strings with decent volume you're a better man than I. This is mega boring to do but worth the effort. I discovered a few years ago that I found these chromatic runs difficult 'cause I kept missing notes out and automatically playing diatonic scales, this I found to be very alarming but it soon sorted itself out.

Once you have fairly strong stretchy fingers try four finger per string scales, these take you further up or down the fretboard for the number of strings you cross too, very useful.