Pachelbel's Canon in D Piano Pages   William Wieland
This repeated 4 bar chord progression is well suited for practicing improvisation.
( D - A - Bm - F#m - G - D - G - A7 )
Printed Music
Mix and match the following suggestions, then - most importantly - invent your own.
Half Notes: Other Inversions | Open Voicings
Quarter Notes: Octave Shifts | Shifts in Inversions
Eighth Notes: Arpeggios | Syncopation