In the 70s in the UK there were actually public information films broadcast to try and encourage drivers to be a bit more wary of motorcyclists.
I'm posting these links not so much to reminisce about that, but because they illustrate how difficult it is to be seen on a motorcycle. Knowing this, you can consider what the drivers in the cars around you might be able to see, and more importantly, what they can't see, and take appropriate precautions. This can involve slowing down when approaching junctions, changing position, and carefully considered use of the horn.
I was pleased to see that these types of awareness ads have come back - I wish they would show something similar stateside.
Two older ones:
http://www.youtube.com/watch?v=oWC8HVDD6AU
http://www.youtube.com/watch?v=J1ZyM7Ihd1k
A newer one:
http://www.youtube.com/watch?v=SXI8-_9FrB4