Excellent response by Roger. I have an extra anchor line of 100 foot length I use for for towing. I make a bridle and attach to the stern eyes for towing from the stern. Be sure that the boat you are towing has an adequate cleat. I was towing a Cal 36 at about 5 1/2 knots (towing with a much larger boat), when a couple of waves out of sync pulled his bow cleat out of the foredeck, and it went flying past our boat--over 100 feet away. There is a lot of power in a tow line--and this is why you see the steel cages between the towing bits and the crew. I advise my crew to always stay away from the points of attachment.
If there is any question about the cleat on the boat you are towing--put a bridle all around that boat--just below the gunnel, and hold it in place with short lines to cleats, or fittings on the boat. This can take a considerable amount of line.
One might ask--why tow someone when there is "Tow Boat US" or "Sea Tow". We have found many places where there is no towing service--for example Lake Powell, we end up towing, jumping a battery or loaning some gas almost every time we are there. Going up and down the Calif. Coast there are stretches not covered by towing services. One time a boat had already called for a tow, before we arrived on scene. The boat's batteries were almost dead, so we stood by until they could talk to the towing service by hand held VHF. It would have been much faster had we towed the boat in, but he had already called for a tow--and the boat took 6 hours to arrive on the scene. We both arrived at the next harbor at about the same time--1AM--we would have gotten there at 9PM if I had taken the boat in tow!