Key word and Boolean searches
Your choice of Boolean operator will yield dramatically different results.
The advantage of keyword searching is that it can produce a good result by boolean searching. Boolean operators such as AND, NOT, OR allow terms to be chosen or excluded. Read the instructions that come with your search engine. The SLCC site above makes it easy by including the help sections of most of the good engines.
Engines differ significantly in the complexity level and syntax used. For instance- AltaVista requires that you use "and not" rather than "not". Spend a couple of minutes and save hours of time by learning to eliminate related topics, group terms together, and specify that keywords must appear within x words of each other.
Remember to substitute synonyms to achieve the desired result.
"Quotation marks" specify that words must appear as typed within the marks. this is a simple but effective way to eliminate lots of chaffin your search.
Plus and Minus Signs
Concept Based searches
Some engines try to determine what you mean, not what you say.
A concept based search returns hits on documents that are related to the word you are searching for. Excite is the best known general purpose engine that employs this method. This technology employs a form of Artificial Intelligence that calculates frequency and proximity of words in a document.