Hanging a hammock from two trees just sounds so darn romantic, but actually doing so can often prove tricky - not every yard has two sturdy trees the right distance apart. The space between trees needs to equal the total length of your hammock, plus 1 foot. So for a 13-foot hammock, the trees would need to be at least 14 feet apart, and so on.
Another option is to hang your hammock between a tree and a single post, or between two posts. In either case, the same spacing rules apply as when hanging a hammock between two trees.
For posts, be sure you use treated wood or some other material that will resist rotting. Posts should be 6 inches by 6 inches in diameter, set 2-3 feet or deeper into the ground. If you know your hammock will be getting a lot of use, it's not a bad idea to add quick-dry cement to the bottom half of the hole around your post. Follow package directions for mixing the cement.
If your trees or posts are correctly spaced, then the hooks for hanging your hammock should be screwed in about 4½ feet up from the ground. To install the hooks, begin by creating starter holes using either a drill or a nail that's 3/16 of an inch or smaller. Once you've gotten a hook started in your post or tree, slide a durable screwdriver through the hook's eye to give yourself more leverage for tightening. Hooks need to be screwed in all the way up to the eye.