Read Social Security and Census Instructions - By Leslie Nelson
When looking over the SS-5 forms you ordered from the Social Security Administration, check out the instructions your ancestors were given when they filled out the form.
Also, one of the best pieces of advice I ever got was to use enumerator instructions to help me interpret census entries. I now routinely look for instructions and background for any record or document I have acquired, and it has saved me from some big mistakes. The site for the enumerator instructions has appeared in the Ancestry Daily News before, but it’s probably worth repeating. This is the website.