Most sites use a hierarchical arrangement.
A hierarchy may be thought of as a triangle, with the home page at the top corner, and the lowest level of detail as the bottom edge of the triangle. If your home page links to twenty pages, you should add another level. Of course, some sections of your site may have more levels than others. This is partly a matter of opinion, and varies greatly from one site to another. Some people believe that lengthy content, which if placed on a single page would require readers to scroll down several screens to see it all, should be broken up into several pages.