USMLE Step 1
Behavioral Science

BRS Behavioral Science covers this subject very well. Pay extra
attention to the psychiatric pharmacology (e.g. side effects of
lithium), developmental stages, and personality disorders.

Ethics is well represented during the examination. Common sense is
not enough.  Memorize the ethics section in BRS. And look for any
ethics questions you can find.  I don't think that reading an extra
ethics textbook/ review is warranted.

The few pages of biostatistics in BRS are also very important. Learn
to handle well specificity, sensitivity, positive and negative predictive
values in a problem-like format. You won't be able to figure them out
for the first time during the actual test.