This is a useful article via Tomorrow's Professor for postgraduate students choosing their supervisory team, with a carefully thought-through set of criteria that includes expertise, accessibility, timeliness of feedback, previous success, personality and attitude to methodology. While the focus is on the rather peculiar North American PhD process that involves committees that both help and assess your PhD, chairs rather than lead supervisors found elsewhere, and talks about archaic practices like the tenure system, the principles all apply well across the board.  If you've already chosen your team (or had it chosen for you) it might be interesting to see how your supervisor(s) match the criteria. Something that is not particularly highlighted in this article is that you don't always need all of these qualities in a single person. In fact, I think it is sometimes useful to have, say, one supervisor who loves your methodology and one that is sceptical, but it all depends on how you like to work.