A technique probably known by most of the people you know, braiding is an incredibly versatile skill. Whether you're doing it to someone's hair, or beefing up a strap for holding something in place, knowing how to braid can drastically improve your ability to DIY.
Step 1: Prepare Strands
You will need to get three strands of whatever it is that you're braiding. This can be hair, rope, or even computer cables. I will tie my ropes off with an overhand knot, but your preference and situation may vary.
Step 2: Braid
The technique for 3 stranded braids is pretty simple. You just need to grab two strands in your left hand, and one in your right. Begin by crossing the leftmost strand over the other in your hand, then place it below the strand in your right. Then take the rightmost strand and cross it over the strand you just placed in your right hand, and place it in your left hand underneath the other strand. Repeat this process until you have reached the desired length.
Step 3: Finish
In order to keep the braid from coming undone, you will need to tie it off. I will be using another overhand knot, but if you are working with hair, a hair elastic would be ideal.