Another question from the Reddit Theory board. Here is my answer.

Ok…here are the simplest extensions.

1. Use the F as a replacement for the F# to convert to the relative minor. D minor is based on F major, so you can also use the C natural and the B flat. https://en.wikipedia.org/wiki/Relative_key
2. Convert the third chord from minor to major. In this case, that is the F#. Add in the A#. Yes, this is the same as the Bflat from the relative minor in step 1, but it is really different sounding. Listen to how Blues Traveller uses it in “Hook” which is based on Canon in D changes. Chords are D A Bmin F# G D G A7 https://en.wikipedia.org/wiki/Borrowed_chord
3. Use the bVII. In the key of G, this is the F7 (natural) . Read up on Back door ii V progressions. It will land back on G. https://en.wikipedia.org/wiki/Backdoor_progression https://antonjazz.com/2012/01/backdoor-ii-v-progression/
4. Add in the #5. This converts the major scale to the bebop scale. I love this note. https://adam.younglogic.com/2019/01/g/
5. Use a tritone substitution: a ii V7 I progression in G is Amin, D7, G. Replace the D7 with an Ab7. https://en.wikipedia.org/wiki/Tritone_substitution
6. Extend the Major 7 chord with the #11. This is the tritone, but it sounds good . The natural 11 is typically an avoid note over the major 7th chord. This is the C#
7. Extend the Dominant 7th chord with the Flat 9. This is the D7 chord, and you add the C#. Yep, same as the one above. This is not coincidence.
8. Create a iiø V7b9 i progression on the relative minor. Again, this is the D minor. It does not really add any notes outside the scale, but the different chords sound good when played with chords beyond the diatonic. The Diminished scale in particular sounds good over the V7b9. So for G major, this would b F#ø B7b9 Eminor. B7 Diminished uses the Half /Whole scale https://en.wikipedia.org/wiki/Octatonic_scale#Jazz
9. Add the major 7th on the Mixolydian mode to get the bebop scale. So, on D7, this is the C#. Seeing a trend?
10. Use the blues scale. This means the Minor third over the major third, the tritone, the dom 7th…all things referred to in early items on this list. You actually have a few blues scales to pick from. The Tonic, the dorian, the relative minor, and the Dom7th can all be the basis for a blues scale depending on position. You’ll find that a lot of the above techniques are actually basic parts of the blues scale, and are much easier to think of as blues tones.
11. One downward running riffs, add in chromatic passing tones to land on chord tones. This is the Barry Harris stuff. IN addition to the #5, you can use the b9 and #9, tritone, dom7, etc…all of the above techniques. When the down beat has a chord tone, the upbeat is very accommodating of non chord and non scale tones.

That enough to get you started?