One of the most popular jazz chord substitution is the tritone substitution sometimes referred to as the dominant chord substitution. The most used is to replace the V with a dominant 7th chord whose root is a tritone below. Example with G7 (V), which can be replaced by Db7 a tritone (Three whole-steps) away. Thus giving two chords that have two notes in common. The 7th of G7 (F) is the third of Db7 and the third of G7 (B) is the seventh of Db7. The inversion of the 3rds and the 7ths between the original dominant chord (V) and the substituted dominant chord (bII7) is the main feature of the tritone substitution.
If the most common tritone substitution involves two dominant chords, there are other chords that can be substituted as the vi chord, the ii chord, and the iii chord. You can substitute any chord which has its roots the flat fifth of the original chord. The type of chord used depends on the melody and the desired harmony. The tritone substitution can also change qualities from the chord it is substituting. Provided that the melody indicates no strong preferences for chord type. For example, dom7 chords can be played in place of minors. This could be subject of another lesson. Meanwhile this article is focused on dominant seventh tritone substitutions.
1- Blues progressions and variations
2- Chord studies
3- Guitar walking-bass studies
4 -Rhythm patterns