The 1930 U.S. enumerator instructions are online, but to answer your question, the date of the census was 1 April, so "persons dying after April 1 should be enumerated, but persons born after April 1 should not be enumerated." Furthermore, "Persons who move into your district after April 1, for permanent residence, however, should be enumerated by you, unless you find that they have already been enumerated in the district from which they came."
As for where to record people, "In general, all persons are to be enumerted at their "usual place of abode" on April 1, 1930. This means, usually, the place which they would name in reply to the question" Where do you live?" This is unlike the UK censuses, which were to record where everyone was on a specific night.
If you are interested in other U.S. census instructions the bureau's website has them online for 1790 to 2010.