"the sociopolitical terrain around here for a new rider"
A fascinating topic. Sommerville and Cambridge...crazy area. I bike and drive in that area, and I'm often dismayed - over the years, I've done a lot of path optimization to minimize my danger spots. Being a bicyclist, I notice how other cyclist put themselves at risk in this area - it's insane, and I don't want to recount all the stories, but driving at night with no bright, reflective or lit gear on very narrow roads, and acting erratically. When driving I become acutely aware of this and I can see how it generates antipathy toward cyclists.
In a way, those 'anti-examples' have helped me ride with more safety. I try to be well lit, avoid narrow roads, notice the choke points and danger intersections, plan my left turns judiciously, taking into account what the drivers behind me will see. Acting predictably, and am generally conscious of being a kind of 'ambassador' to drivers for other cyclists - not running reds, stopping at stop signs and all that good stuff that cyclists get dinged for.