harmonize each note with another note three pitches above it in the scale being used. the riff you suggested is in the Cmaj or Am scale. So, play the A with a C, the B with a D, C with E, E with G, F with A. Alternatively, you could harmonize with fiths or sevenths
Last edited by gimli323 at Mar 11, 2007,
^What he described is a diatonic thirds harmony, but you could do anything. You don't even have to use notes in the A minor scale (at a glance, that looks like an A minor riff). I think thirds could be a good way to go (it usually is), so the harmony would be C D E G A G A.
Please run a search on harmonizing. There are many threads on this subject. Some have been recent as well