The 1940 Census will be made available for public inspection beginning Monday, April 2, 2012. The U.S. Census Bureau and National Archives and Records Administration (NARA) have been coordinating closely for many months to prepare for and ensure access to the 1940 census schedules as quickly as possible. NARA has already announced the completion of a digitization project and their plans to place all images online for free browsing via the Internet. Although there will not be an index immediately available to search by name, a little preparation can increase your chances of finding your ancestors in the 1940 census without much trouble.
Start by listing those direct-line ancestors who you have found in the 1930 census and that you know were still living in 1940. While it's possible that they may still be living in the same city or state, don't rule out the fact that your ancestors may have moved. Once you have listed these individuals, consider looking for anyone in their mid-to-late teens or 20s who may have been living in the household in 1930, but may now be found as a head of their own household. Next, you'll want to repeat this same process for indirect ancestors (aunts & uncles).