Step 2: 2 Monkeys fist
You can tie a "Monkeys fist" knot as seen in the picture below. If you want to tie this there are many places on the internet you can find instructions for it.
Step 4: 4 Leash/Collar
Another way to reuse rope, if you have a pet, is to make a collar/leash combo.
Step 5: 5 Necklace/bracelet
You can also make a bracelet or necklace by burning the two ends of the rope together.
Step 6: 6 Rug
A rug is very easy to make with old rope, you just need to burn the rope together on both ends and places in the middle.