ok so im trying to write a song and ive come up with a riff, but i dont know how to harmonize the second guitar. is there a certain way like changing octaves or just coming up with something to go along with?
It all has to do with the intervals on the particular scale you are using. Many artists use 3rd interval harmonies, which means it is the third note in the scale above the original riff. If you are unsure of the scales you are using, it is worth investing the time into learning scale forms. Good luck!