How can you avoid a picking a bad adviser if you’re not sure what you’re looking for in the first place?
One way is to study what goes into the decision. Be an informed consumer: Know what you want, and expect what you’re entitled to.
From the comments
Spotting (and avoiding) a bad adviser is actually much easier than finding a good one. Common issues to watch for:
(1) Ask: find former students or colleagues and [delicately] ask whether (s)he is an effective adviser who supports students.
(2) Speak: is (s)he someone with whom you can truly speak... candidly? You will need that later on, so avoid those aloof, cagey, dismissive, and distant personality types (and yes I realize that probably rules out half of academia);
(3) Publications: does (s)he publish results regularly? If not, avoid. Remember you're there to do work and get published.