U.S. Government websites end in the domain names .gov .mil http://google.com
Top 10 
Tips
10. Get specific with quotes (""). Quotes creates a phrase search
9. Search within a specific website (site:)
Search within a particular website, or web domain. Use site:gov or edu...
8. Subtract terms you want to exclude (-) Subtract terms you do not want to appear in your results: surfing -hawaii
7. Add terms you want to include (+) The opposite of - would be to use +
6. Use the Advanced Search Page
Get advanced!
5. The OR operator
Using the Or operator between words allows you to search for synonyms and spelling variations. The following example will search for "Eddie Aikau or surfing."
4. Specific Document Types:
You can limit your results to certain file types. These file types include PDF, PowerPoint, Word Document and Excel Spreadsheet. filetype:pdf
3. Get specific by searching within a url. Use - inurl: or allinurl:
2. Get specific by searching within a title. Use - intitle: or allintitle:
1. Find similar words with tilde (~). If you would like your results to contain similar words or synonyms use the "~" in front of the word. Example: "Surfing " ~professional