When using http://Google.com to search for family history data, here are a few tips to bear in mind:

• record what search terms you tried (eg “John Nelson Ireland reverend”) in deadeasyfamilyhistory.org, or wherever you keep track of your research progress (this way you’ll remember what you already tried)
• also record the urls of any websites of note (you might want to retrieve them later)
• try using longer search terms. Eg if you want to search for stories on a relative named “John Nelson” who lived in Belfast, Northern Ireland, between 1850-1920, who worked as a Methodist minister, don’t just use “John nelson” as the search term in Google. Try “John Nelson Belfast ‘northern Ireland’ Methodist minister 1850”. If nothing turns up, try generalizing your search by removing words
• if you get too many results, or results that are clearly for something else, try excluding those results. You can add a minus sign in front of a word to tell Google you want to exclude results with that word somewhere on the page. Eg if the above mentioned search somehow turns up a bunch of sites relating to football, you could add “-football” to exclude those football related sites
• use quotes to search for words in a specific sequence. Eg if you’re searching for an ancestor with the first name Nelson and the last name Williams, but keep getting results for people “William Nelson”, try putting quotes (single quotes or double quotes, both work) around “Nelson Williams” to tell Google you don’t just want pages that have “Nelson” in them somewhere and “William” in them somewhere, but instead pages specifically with the name “Nelson Williams” in them
• if you know you only want to see pages from a specific website, use the site’s name followed by a colon. Eg “deadeasyfamilyhistory.org:”
• use google alerts. Go here for more info 

Most of the above suggestions originally came from this family search blog post.

Be sure to comment on this research tip if you have other suggestions on how to use google for family history research