I usually give handouts with chord diagrams and start in the key of G, and do the chords: G, C, D or D7. I (briefly explain the concept of I, IV, and V7. I make sure the attendees are fingering the G chord correctly with the middle, ring & pinkie fingers only! I show them a few basic strums, to include the alternating bass note strum in 4/4 --where you pluck the bass note with your thumb on 1 & 3 and pluck some of the other strings (or strum!) on 2 & 4 as well as 3/4 bass-strum-strum (this "no pick" style is very good for playing Irish music! If they are not into fingerpicking, just let them strum with picks) and how to use a pick to do all that, too--with diagrams of which bass note of the chord to pluck & when to pluck & strum. If they are catching on quickly, then I show them the Carter Scratch, and possibly a couple of other strums, depending on how well they are catching on. Fingerpicking & Hammer ons, and pull offs only if they are advanced enough, but you never know who will show up, & knowing what. Some of the info will be above the heads of some & not of others. Then I like to have them experience the feel of strumming a couple of different kinds of music such as basic 4/4 country or 3/4 waltz & maybe a 6/8 jig. I like to take extra materials with me just in case. Tell them it's OK if they don't get it all that day, cause some things take a while to learn! Leave them with something they must work on to accomplish, but let them have fun. If they don't have fun, they won't like it. You might consider going to a music store & taking a look at at the "Mel Bay CLASS METHOD" Volume 1. It is the best comprehensive book I have found, and very easy to understand. I have used it about 30 years for private guitar lessons.