What to play and where:
Before you venture into any attempt at navigating chord changes, you need to know what scales to use, and where to play them on the fretboard. But that's not the subject of this post, so if you have trouble with that, I recommend using SFS (string fragment system). SFS is an extremely effective way to map fingerings anywhere on the fretboard without memorizing fingering shapes. The example video below is an excerpt from SFS Pentatonics 2 - Navigating Chord Changes.
Assuming that you already know what scales you are going to use, the process is very straight forward. Select an area on the fretboard, choose what fingerings you are going to use, and then follow the 3 steps listed below:
1. Roots Only
Just play the root note of every chord. It's a good idea to think (or call out) the full name of the scale while doing this, especially if you are dealing with a song that uses a variety of scale types and modes.
2. Scale exercise
We are not improvising yet. Just play the scale up and down, as an exercise. If you want, you can split this step into ascending and descending, in order to get used to starting melodies in both directions. If the changes are flying by very fast, you may have time to play just a small part of the scale, which is fine.
3. Improvisation
Now you're ready to use your imagination and play freely. Again, if you see that you have a tendency to always start in the ascending direction, you may want to split this into two parts, in order to play phrases starting in the descending direction, on purpose.
Demonstration using pentatonics over random dominant chords:
You can apply the same process for pentatonic scales, 7-note scales, arpeggios, and any kind of structure that you like to use in your solos. Check out the EMP Backing Track Library for Key Cycle Backing Tracks that are designed specifically for learning to navigate chord changes. So try this in your own practice time and let me know how that works out :-)