In the June, 2012 "jamming" issue of Banjo Newsletter, Hugh Strawn writes:
"I've had some experience with jams over the past 20 years and in those years I've experience behaviors that should be emulated and behaviors that should be admonished (that is, directly admonished, because some of them couldn't merely be ignored other than by walking away, and I've done that).
"I might add there is only one type of jam which I am really comfortable with and enjoy. This jam is alpha-fiddler led (tunes may be suggested by all), all fiddle tunes -- no singing, all instruments 'back' the fiddle, no individual breaks, stay in one key for 3-+ minutes, play tunes for 5+ minutes, and consists of participants who respect the established structure of the jam and don't try to change it."
Truer words were never written. Especially the alpha-fiddler requirement.
Dan Levenson is my favorite alpha-fiddler. Dan also has an article in the same issue, in which he writes about his role as a "jam workshop" leader in Yuma, AZ. It's very different from his role as an alpha-fiddler.
Most of this particular BNL issue is about bluegrass jamming, but these two articles are great.