Mary Ann asked me about the ingredients of a sketchcrawl so she could put one together in Boise, ID. My response:
Sketch Crawls are based on the model of the pub crawl. Go to a place -- draw (or drink) -- and then move on to the next spot and repeat until you fall to the ground. As such it is a fairly loose proposition. I think it's best when you have a range of different drawers of

different experience and skill levels but I have done most of my crawls with just one or two people. I've even done them alone (sob).
In a small group we've tended to draw the same subject some of the time and spent 20 minutes or so per drawing. When we're all ready we move on. Occasional stops for libation are an important part of the process. Three-hour ones are okay, The best are, like, six- or seven- so by the end you are completely drained and have a whole bunch of new drawings. Usually we are all mute with exhaustion by the end.