A system of consistent and clear navigational markers can help users quickly recover their bearings. Assume the user is a web novice. Their web skills will be few, and much that expert users take for granted is counter-intuitive to the newcomer. Assume the user has a slow connection. Be mindful of download time.
Web sites are normally in a constant state of development.
In their earliest stages, there is rarely provision for growth. Over time, the result is a bewildering hodge podge. Groupings of information and connections between them stop making sense. In the life of any growing web site, there comes a time to take it all apart and restructure it around a single organizing principle. Know your focus.