umm well you need to be in a scale, and just write parts of a riff / solo in up / down a specific number of intervals. im pretty sure 1 - 2 and 1 - 7 are dischords, so you can create some pretty stark harmonies. the rest (1-3,1-4,1-5,1-6,1-8) are all major harmonies (i think that's what theyre called), so theyll sound nicer. BTW the numbers are intervals of a scale ^^

btw it's spelt 'harmony'