Find a branch that will support your swing safely. A good branch will be about 12 to 15 feet off the ground, six or more inches in diameter, and long enough to hang the swing about three feet from the trunk. You want to be able to hang the swing with enough clearance from the trunk for safe swinging, but not so far out that it could overstress and snap the branch.
Drill two holes in the branch that will be slightly larger than the size of your eyebolts. The holes should be spaced a few inches farther apart than the length of your swing seat. If your swing is 26 inches, the holes should be spaced about 32 inches apart. This will help keep the swing straight and keep the ropes from twisting around each other.
Place an eyebolt in each hole with the eye of the bolt on the side of the branch that faces the ground. Secure each eyebolt with a washer and two nuts. The first nut will secure the bolt in the branch, while the second bolt will help insure the first one remains secure. As the tree ages, it will grow around the bolts and possibly the nuts.
Hook a carabiner into each eyehole. It is important that you use carabiners rated for climbing so that they will hold up to the weight of the swinger. There are many carabiners sold as keychains or clips that will not be able to support a person's weight. Make sure you do not use this type of carabiner. The weight rating should be located on the carabiner.
Tie a loop in the ends of the ropes you will be using to hang your swing. Attach one rope to each carabiner by clipping them through the loop.
Cut the ropes to length so that there will be enough clearance beneath the swing for the swinger's feet.
Attach the hanging end of your rope to your swing seat. You will now have a safe and secure tree swing that will provide you with years of enjoyment.