You've got to remember the basics...

Ancestry.com saved me from a stupid mistake of not following one of the basic premises of census research: I didn't look at the rest of the page while searching for my Grandmother's natural parents. I was looking in the 1920 for Harry Williamson, with his unnamed wife (who's maiden name was Hambst), and either one or both daughters: Claire or Francis. Using Ancestry.com's great search feature, I found them fairly quickly (see line 29-31 of the attached photos), even learning that my natural great-grandmother's name was Theresa:

Even though I store very little of my research on paper by putting most in the computer, I do like to pull out a census form and copy everything down so I can think about each item. So that's what I did. But, I never looked around the rest of the page. Luckily for me, as I was backing out of the form, I noticed that Ancestry.com had three other people listed as part of the household. Duh! So going back into the form, I quickly realized that not only had I found my natural great-grandmother, but her mother and two brothers (see lines 32-34 for Walburga Hambsch and her sons Anthony and Peter). Wow. What luck!