Inspired by previous conversation, I'm on Ancestry.com and I'm so frustrated. Now I remember why I quit using it before. I found my father in the 1930 Census - he was 7 - and I'm trying to get information on his first marriage. I entered all the information I have on him, and it's returning thousands of search results from everywhere, like Australia and Wales, places where I know he never went, and nothing from Michigan or any state where I know he lived. So in order to get more information, apparently I need to have more information.
You can restrict your search by country, and then dive deeper from there. If you know the approximate year of his first marriage, add that in, as well.
1940 census data comes online in April, I believe. Not that it will help me, being the first born American citizen and all.