Aside from keywords themselves, are there settings in AdWords that are known to produce, on average, poor traffic where visitors immediately leave the site etc.? For example lower bids affecting traffic quality or does that not matter?
The biggest thing that matters for my google ppc campaigns are ad CTR & quality scores. If you're quality scores are pretty good, then that's googles way of telling you that you're getting the right traffic to the right web page. The better your CTR, the lower you'll be charged for clicks so just aim for those two. I can't really thing of anything else at the moment in terms of traffic quality but bidding on the right - targeted keywords obviously is important too. Good luck!