Embellishing extended dominant series
You can use tritone substitutions and related IIs to spice up your extended dominant series.
Start with a basic ragtime progression:
E7 | E7 | A7 | A7 | D7 | D7 | G7 | G7 | C
Then replace the second occurrence of each dominant chord with its tritone sub:
E7 | Bb7 | A7 | Eb7 | D7 | Ab7 | G7 | Db7 | C
Then for every dominant chord, add its related II in front of it:
Bm E7 | Fm Bb7 | Em A7 | Bbm Eb7 | Am D7 | Ebm Ab7 | Dm G7 | Abm Db7 | C