My friend Erin had another question, so I thought I'd share the answer with everyone.
Do they tell you what to put in a proposal? Where do you even begin?
I'll start with the where do you even begin (as far as proposing) part. Seriously, the internet was my best friend in figuring out where to start. I sort of stalked the teachers from Artfest on their blogs and websites to see where they were teaching. I looked up the blogs and websites from the events and figured out contact information. Then I emailed the event coordinators to ask for an application or for submission information.
I think if there's a location nearby to you that offers classes, you could just email them to ask about how they pick their teachers.
The submission part varies by event. Here's my experience so far:
Contact: Teesha Moore
Last year, Artfest asked for photos of four samples of each project. This year, they are are asking for at least multiple samples rather than specifically specifying four samples. They also ask that you fill out a workshop proposal form for each project. You have to mail in the packet of photos (I did nice, large print outs from my inkjet printer) and the workshop proposal forms. You also send a brief biography.
Art & Soul
Contact: Glenny Moir
Art & Soul prefers that you send in actual samples of the project, but you can also send photos if you'd like. Last year I sent samples. This year, I sent photos. You also fill out a workshop proposal for each project to send in too.
Art Is You
Contact: Sallianne McClelland, Ellen Purtill-Legare
Art Is You is a little different. They just ask that you email photos of samples of your work. They decide to accept you as an instructor based on your samples, and then when an event comes up, they ask you to submit proposal(s) for workshops.
Contact: Cindy Mayfield
Paper Cowgirl asks for submissions via email. There isn't a specific application form, but the same basic info is needed - description, supply list, class fee, etc.
Inspire My Life
Contact: Kim Geiser
Inspire My Life retreat asks for submissions via email. Again, no specific application form, but you'll need the same basic information.
And of course, the list goes on. Those are just the ones I proposed for last year. For 2012, I'm going to try to expand to a few more.
About workshop application forms...
In case you're wondering, the application forms aren't intimidating at all. They ask for very simple, practical information like a workshop description, the supply list, kit fee (if any), maximum number in class, and some ask for the amount that you charge. If there are evening or partial day classes at the event, the application asks if your class is 6 hours (full day) or 3 hours (partial).
If you have more questions, ask 'em! :)