Chris Michielssen recommends the Uni Knot for tying shock cords. Here’s a graphic showing how it’s tied. For fishing line you need five or seven wraps but for thicker cords, Eero Fluge says you can use three or four wraps for a cleaner knot.
I’m telling you this because actually I’m telling me this. If I post the link to the graphic, I’ll know where I can look it up.