Keep it simple. If you're looking for a particular company, just enter its name, or as much of its name as you can recall. If you're looking for a particular concept, place, or product, start with its name. If you're looking for a sushi restaurant, just enter sushi and the name of your town or your zip/postal code. Most queries do not require advanced operators or unusual syntax. Simple is good.
Think how the page you are looking for will be written. A search engine is not a human, it is a program that matches the words you give to pages on the web. Use the words that are most likely to appear on the page. For example, instead of saying "my head hurts," say "headache" because that's the term a medical page will use. The query "in what country are bats considered an omen of good luck?" is very clear to a person, but the document that gives the answer may not have those words. Instead, use the query "bats are considered good luck in" or even just "bats good luck" because that is probably what the right page will say.
Describe what you need with as few terms as possible. The goal of each word in a query is to focus it further. Since all words are used, each additional word limits the results. If you limit too much, you will miss a lot of useful information. The main advantage to starting with fewer keywords is that, if you don't get what you need, the results will likely give you a good indication of what additional words are needed to refine your results on the next search. For example, "weather Vancouver" is a simple way to find the weather and it is likely to give better results than the longer "weather report for Vancouver Canada."
Choose descriptive words. The more unique the word is the more likely you are to get relevant results. Words that are not very descriptive, like "document," "website," "company," or "info" are usually not needed. Keep in mind, however, that even if the word has the correct meaning but it is not the one most people use, it may not match the pages you need. For example, "celebrity ringtones" is more descriptive and specific than "celebrity sounds."
NOTE: The following guidelines were adapted from Google's Help site for Safehaven.com's vistors.