Forum Moderators: open
1. Keep the link structure as shallow as possible. Try for 2, or on a big site 3, clicks from the Home page to any other page.
2. Try not to nest directories very deep -- even if the information architecture looks like it goes many levels deep, these levels can all be in a top directory. Not nesting directories keeps your URLs shorter.
3. All pages should have at least 1 inbound link that is "straight text" HTML, not an image, not javascript, not cgi, no query strings etc.
4. Cross link your pages well. Try for 2 or three clicks from any page to any other page.
5 Have a site map, but if it gets to be more than 100 links on a page, break it into 2 pages, then 3.
These are ideals for me, and I don't always follow them all. But the closer I come, the more throughly the site is crawled.