Let me note at the onset that this instructable is not a joke. It is long and detailed, with lots of pictures. If you're really not interested in building a tire swing, then don't waste your time looking through it. But, if you are truly interested in building a tire swing, then this is serious and detailed instructions that ought to give you every tool to be successful. Good luck!
Step 1: Pick out a tire!
Once the tire is chosen, look at both sides of it and determine which side looks better. This will be the top side. Flip the tire over and drill holes in the bottom sidewall. To do this, set the tire on a surface that will be at a height appropriate for drilling without straining your back. I used our new picnic table & it did the job perfectly. Use about a 1/2" drill bit and drill holes around the sidewall, ever few inches. The holes don't have to be perfectly spaced, but it'll drain better if the holes are more evenly spaced. I used the tread pattern to space the holes. Here's a picture of the bottom of the tire with the drain holes already drilled.