A technique that has proven useful to me is to run barefoot on pavement and gravel. The roughness of the surface maximizes the sensory input to your feet, and the hardness of the surface calls attention to any excessive impacts or inefficiencies further up the foot/leg/knee/hip joints. I often run the first mile or two of a workout barefoot on pavement as a way to maintain a "muscle memory" of good form.
You can start by standing on the pavement or gravel, getting a feel for what the surface feels like "at rest", and then walking in place for a few steps, then bouncing and jogging in place, and then begin moving forward. As you transition from standing to moving in place to running, pay attention to how the surface feels on the soles of your feet, how your feet are landing and lifting, how your muscles and joints feel. I've found that even very small adjustments in foot placement, hip movement, knee bend, cadenece, etc., are can be measured by watching for changes in the level of comfort or pain felt on these sorts of surfaces.
But this is a rather subjective technique that I think is only useful in conjunction with learning about good form from other sources, etc. Thus I would be very interested in seeing a more thorough answer than this that describes some more objective techniques to self-assess running form.