Specifically in the case where I don't know anything about the documents I'm working with. I'm looking a specific number or number range.
Griffiths and Steyvers (2004) suggest a value of 50/k (where k is number of topics) for α and 0.1 for δ. (They use δ rather than beta to refer to the other hyperparameter).
Griffiths TL, Steyvers M (2004). “Finding Scientific Topics.” Proceedings of the National Academy of Sciences of the United States of America, 101, 5228–5235.