You can use a minus sign next to a word you want to exclude. For example, if you want to learn about dolphins but are frustrated by all the results about Miami's football team, search for dolphins -football.
You can limit your search to a specific web site. For example, if you want information on ethanol from the Wall Street Journal, search for ethanol site:wsj.com. You can also limit your search to a specific category of sites, such as site:.gov or site:.edu.
A wildcard allows you to search unknown words. For example, you can search for harkin voted * on ethanol to see how Iowa's senator voted on this issue. You can substitute the wildcard for more than one word; for example, you can try a search for grassley voted * on * to see different bills.
NOTE: You can only use the wildcard for whole words, not parts of a word.
In Google, you can limit your search to a specific file type. Simply add filetype: before the file type you want. For example, you remember seeing a great eggplant recipe once that was in PDF format. Try searching for eggplant recipe filetype:pdf.