Where, and how, you get the word out that you're holding a Slow Jam will depend on what kind of people you want to attract. Rather than speculating about what/how you should do it, I'll just suggest you think on it before you start "hanging flyers." If you're doing it as a "class" for an "established institution" then you may not have too much choice about who shows up, but you should be prepared to "theme" things from the beginning.

It helps to have a "style" in mind. It does matter whether you're doing an Irish, Country, Rock, etc. session. You don't necessarily need to be too selective about letting in people with other interests, but it will greatly improve your odds of getting a group formed if you let people know that you intend to concentrate on a particular kind of music.

Specializing on a particular instrument can sometimes be a help in attracting a core group of beginning to intermediate players. Our local "Dulcimer Alliance" has been having monthly "slow jam" sessions, with a fair turnout of mostly regular participants, for several years now. The idea of a Slow Jam is for people to learn something, and it can be helpful if everyone is working on the same (or at least similar) things.

You should pick a couple of pieces in advance to introduce for each session and have sufficient copies LEGIBLY printed for handouts. You may have people who don't, or won't, read dots. Don't press them too much, but make them take a copy anyway, so they'll remember what pieces have been "studied."

Hopefully, you'll have someone who can play the "new" piece(s) respectably, but at a speed that doesn't dazzle the "students," and who is willing, if needed, to play them over and over and over and over....

If you get things going, you should keep track of the songs that have been introduced and always try to go back and play the "new" stuff from the previous session or two. It can give people a real feeling of accomplishment just to recognize something they saw for the first time recently, even if they still don't feel confident about their playing.

If you find a song that nearly everyone can play, and enjoys, consider making it a "theme song" - perhaps for the closing number, so that everyone gets a chance to do well at least once per session.

If you're in charge, you may have to be cold-hearted cut-'em-down drag-'em-out CRUEL, if someone gets too far out of line. On the other hand, if your rules get broken, but everyone seems to be having fun - toss the rules.

Most people won't come back if it hurts. (Applies to those you want, and those you want to get rid of.)

John