Everyone who has a web site want as much traffic as possible and for them to stay for as long as possible. One way to do this is to offer a free ebook. This will keep them on your site as they take time to read it. If you content is put into a story format, most people will be interested in who it ends and so they will stay and read it through.
If your site has a chat room, then your visitors will be able to talk with other with the same interest and this can take time for sure. People generally like to talk and not just about the weather. Hook up those with similar interests and you create friendships, from your site.
Is your web site offering many things to do? Keeping people busy keeps them on your site. Let them add their link, play an interactive game or sing your guest book. All these busy things will keep them on your site and return later. You can also set up a FAQ part of your site. Those who ask a question, will most likely remain waiting for their answer. Reading adjectives will keep you visitors focused, so use many of them in your content.