The Alpine Butterfly Loop is an incredibly useful replacement for just grabbing a chunk of rope in the middle of a line and making an overhanded loop. Load can be applied in any direction on any of the pieces without it slipping or coming undone.
Step 1: Prepare to Tie
You will need one piece of rope. Make sure you pick a spot to place the loop, as well as one end with which to tie the knot with.
Step 2: Tie the Alpine Butterfly Loop
I had a particularly difficult time explaining this knot, so I'm quoting one of my favorite sites, animatedknots.com If you are interested in furthering your knot tying skills, I would highly recommend checking it out.
"Wrap the rope around your hand twice. At the end of turn one, position the rope close to your fingertips. Continue around and complete turn two back near your thumb. Pick up the turn near your fingertips. Wrap it around the other two turns. Slide the knot off your hand and tighten by pulling on the loop and the ends."