1. Everything is on the Internet.
2. The Internet contains nothing but trash.
3. Anything on the Web is findable.
4. Search engines search the entire Web.
5. The Internet is the Web.
1. Web page just posted and spiders haven't indexed it yet.
2. URL expired.
3. Web page inadequately indexed by search engines.
4. Bot blocker in effect.
5. Site not completely indexed.
6. Problems with alpha or numeric address.
7. Site is a dynamic site: permanent Web page does not exist, but is generated "on the fly."
8. The URL is case sensitive.
Internet addresses are really a series of numerals, but can be aliased with easy-to-remember alphabetic addresses. These alpha domains are usually easy to distinguish. A list of all domains can be found at: Domain Name Registries Around the World. Common domains include .edu (US educational), .gov (US government), .org (US organizations, usually non-profit), .int (international organizations), and .us (US state and local entities).
With Google, enclose phrases in "quotes". This forces adjacency and limits the results. Ex.: "joint committee on printing".
Often it is helpful to limit your search to a specific file format such as Adobe Acrobat (PDF), Word (DOC), PowerPoint (PPT), Excel (XLS), etc. To do this, type filetype:[extension]. Ex.: digital divide and filetype:ppt.
A powerful way to restrict search results is to limit by Internet domain. For example, you could restrict results to educational domains (.edu), to government domains (.gov), or to Canada (.ca). To do this in Google, add site:edu to your search to limit to US educational domains.
Another useful trick is to search a secondary-level domain. To search for information on Museum Studies on University of Denver sites, search like this in Google: site:du.edu museum studies.
This strategy is very effective when looking for authoritative information from known Web sites such as un.org. To search for information on "child soldiers" from the United Nations site, search Google like this: site:un.org child soldiers.