Electric guitar...

OK, I'll start.....

My first riff was "Paranoid" (what, not "Smoke On The Water"??).

My uncle spent about an hour and a half showing me the Black Sabbath chord and how to hold that shape and hammer on for the riff, as well as move the chord both on the same strings but different frets and in the same position, but one string down, then told me to go home and practice.

It was an interesting approach as it covered several bases at once, but not overly complex.

What really hooked me was the octave of the open E string that you can play (but is not necessary for practice) that really gives a full and ominous sound.