In his comments to my blog entry on internet search fundamentals Shally referenced a great article titled Keyword Mutation Detection and the Art of Seeking. In it, he mentions MS’s AdCenter Labs and the use of the tilde (~) which are some great suggestions to help you expand your search
What helped me to understand their importance was coming to understand that search engines simply see keywords as a set of characters strung together. Search engines don't base results on how we use language. They can recognize groupings of characters/letters and identify them as words but they don't link them to a thesaurus database to give you some associated words unless you specify. That is why if you search for the keyword “Children” the keyword “kids” will not be included in the results.
In order to harness the fabulous power of search engines don’t assume that there are any related concepts to your keywords. Be sure about how your keyword will interact with the search engine. A great tool for that is google’s synonym lab be sure to try your keywords there for related concepts. The limitation to using synonym searches is that the thesaurus database used gets outdated or may be incomplete. That is why it is better to learn to refine your search through the use of alternate keywords. That is were MS Adcenter’s keyword group detection is helpful.
The toughest problem in crafting queries is learning how specific does the query term need to be. If we use too broad a keyword too many results are returned; if we us too narrow a specification, too few are returned. Finding the right level involves your personal knowledge and experience.