You need to be careful with clove hitch, it's a great knot, but it can fall off if the rope gets slack.

I'm interested in what knots/skills you use to do things like keep your headphone cords untangled.

I usually simple butterfly coil w/ wrap finish around my index + ring ringers. There's a bunch of different approaches people use; the general ideas of not introducing twists (not a big deal for short cables) and finishing with a wrap are more important than any One True Way.

Specific to headphones and other cords: avoid introducing sharp bends as well -- cheap cords will eventually short out. (For me, I try to have a fairly fat "bundle" before I do the wrap, and don't pull it too tight.)

Use a figure-8. It's easy to tie and untie and it doesn't have any sharp bends to risk kinking the wire.