One does not contribute to the development of the research or the software itself, but one helps others that don't know how this is done with the Open'ing aspects.
Of course, I know that there are several online resources for learning, but what beats a mentor who dedicates some if his/her time?
Thanks Adam! The @osgeo mentorship programme, albeit way too ambitious for me at this stage already has some good description of what they are looking for in #OSS, including actual community contribution (guidelines, governance, ...)
I am aware mentorship like consultancy has a cost, and I am not against the idea.