Do you know what key the music is in? Usually you can arrange the accompaniment by improvising the chords. Most accompaniments are written in some sort of inversions and rhythm patterns.



Yoke Wong
Mastering Piano Accompaniment
http://www.howtoaccompany.com

I don't write much of my own music, however sometimes I do like to change others for a different and unique feel. I find it easier if I record a single note melody, then play it back while I "experiment" on it!

Yoke is quite right - knowing what key it is in is a great place to start...somewhat an endorsement of regular notation!

If you mention the notes (in the order the occur) I can suggest a possible start on harmonizing your line.