As a researcher, once you are depositing your papers in a repository, support your institution (if it exists) in adopting, monitoring and enforcing the deposit policy. What else can and should you do?
Spread the word to other researchers encouraging them to follow your lead. Encourage your government to adopt a policy that all research institutions receiving public funds should adopt the deposit policy. Encourage funding bodies to adopt a compatible deposit policy. 1 Where your papers are closed access due to publisher restrictions, promptly use the button to send a copy to the requester.
If you are an editor, editorial board member or reviewer for a journal or conference, consider their open access policy. If they do not allow open access deposit, consider dropping your involvement with them (and explaining why), but only where this will not harm your career. Tenured professors in particular are in a good position to remove their kudos from supporting regressive publisher policies. Expecting junior colleagues to give up roles which are necessary for their tenure or promotion processes is not reasonable.
If you are a member of any scholarly societies which publish journals or reviewed conference proceedings propose that they allow deposit. Do not be distracted by claims that their publishing income is necessary for their scholarly activities. Do not let the publishing tail wag the research dissemination dog even for scholarly societies.
Continue to serve as editor/reviewer/editorial board member for journals and conferences which allow repository deposits.
Do not try to change journals to Gold OA.
Do not pay "Hybrid Gold OA" charges. The publishers' costs and profits are already being generously paid by subscriptions. Providing access to your papers in a repository is a better way of providing OA, since it is applicable to all your papers and all those of your colleagues and peers as well. Do not support governments or funders in any proposals to promote paying for these charges.
Do not start a new Gold OA journal just to provide a Gold OA route. New journals should be started because there is a need for a new outlet for work not well-served by current journals.
Do not try to change copyright transfer policies by not submitting your articles to journals which require a transfer. Do not try to impose such a policy at your institution. Do not support a government or funding body in their proposals for such a policy.
1 In particular, funding bodies should require deposit in the institutional repository and if they deem it useful arrange for central harvesting from central subject repositories of institutional deposits. That way multiple funder policies reinforce local deposit and central collection and provide a coherent single-locus of deposit for their researchers, instead of a complicated game of "where do I deposit this paper" for each different paper, particularly for those including work funded from different sources.