If you are very good at making greeting cards, I would start with that - people love doing that. Do you use a basic software that people could easily buy? They will need to be able to replicate the project at home also. There are so many software applications out there.

I would make a greeting card and write down all the steps it took to make it. You have to remember some folks have to idea what to do. So if you are importing graphics - you have to explain it step by step. I would have a "cheat sheet" of instructions made up for them to take home also.

Maybe you could have a sample card made up and attach it to a flyer about your classes.

What a about a "make and take" class. You instruct them, but they also get to make 6 cards and envelopes to take home?

You could do photo cards - have them bring some of their photos they want to use and show them how to print them out in smaller sizes and then mount them on a couple different colors of cardstock, then to the card. You could print some things on the inside of the card first, or "created by ****" on the back before attaching the card.

You might also do a free practice class with someone just to see how it goes.

Remember all the copyright stuff - you can't give away software or graphics - but there is some freeware stuff out there to download - you could give the address to the students and they could d/l it at home.