These temporary rules principles are something I use frequently for my clients as well as for myself. They are a great way to break out of your regular routine and force you to look at things from a different angle. For the next few days when soloing or creating melody lines, only use scales that are relative (sharing the same group of notes or key signature) to the primary key that you are in. For example, the solo for Smoke On the Water is in G minor or G Aeolian. The solo starts by using G minor 15th position. Then that first quick run at about the 3:10 mark basically uses the C Dorian form in 8th position. C Dorian is relative to G Aeolian, so he never really leaves the original key, yet uses a scale form that can be defined as relative. Make sense?
Here’s another example. If you were soloing over a section that is in A minor or A Aeolian, and you usually play A minor pentatonic licks, shift to playing only D or E minor pentatonic scales. Here’s why – A Aeolian, D Dorian and E Phrygian are all relative (no sharps, no flats). Also, all three modes contain the required spelling to make a minor pentatonic scale (R, b3, 4, 5, b7). However here’s the cool thing – the notes in A minor pentatonic are A, C, D, E, G. The notes in D minor pentatonic are D, F, G, A, C. Notice two things here, first you are still true to the key signature which is no sharps, no flats. Second, the selection of the notes you chose is slightly different, not completely but slightly. When you play your usual minor pentatonic licks in a relative key, they will have a slightly different feel, or texture. That’s your challenge! Go experiment with it and have fun!