Ensure your publishing agreement allows the paper/manuscript to be posted to PMC (PubMed Central) in accordance with the policy. Before you sign an author agreement or copyright transfer agreement, make sure the publisher allows the paper/manuscript to be submitted to PMC.
There are a few places you can check to find information regarding your publisher's stance on PMC:
Harvard's open access policy "operates automatically to give the University a nonexclusive license in any scholarly articles a faculty member completes after its adoption." Harvard has a generator that will create an "author addendum" to attach to the agreement with your publisher to "avoid a conflicting transfer of copyright to the publisher and to protect yourself from breach of contract."
Gold Open Access Policy
Green Open Access
*Embargo period: a specific amount of time determined by the publisher before the full text of a manuscript can be accessed by the public without paying for it.