Before going backpacking last year, I decided to learn a bunch of knots while I was watching TV and relaxing. It was really helpful during the trip; I'm usually a "use a variation of an overhand or square knot for everything" type of person, but knowing a few specialized knots was really helpful when setting up camp (securing tarps, hanging hammocks, attaching gear to the bag).

This is my favorite knot, its called the midshipman's hitch on animated knots but I knew it as taut-line hitch from my book: https://www.animatedknots.com/midshipmans-hitch-knot