The girls all have really good advice for you. Do you have the Extreme Elements stamp set? It is a great one to demo on a scrapbook page because it is different from other set, almost foolproof and you can just layer any stamps from the set to create a unique background. (See example here:
Rock Star Wannabe)
Don't let scrapbooking intimidate you. Just think of it as a big card: the picture is your main stamped image, the title is your sentiment and you embellish just like you would a card.
I think the new Sweet Pea felt embellishments with matching papers are another great accent to show. They are beautiful and definitely something a scrapbooker would love, I would think!
As for the format, I would recommend going for either a 6 x 6 or a 8½ x 8½ page so you don't feel overwhelmed and you can keep your costs to a minimum. You can cut those two formats out of your regular 8½ x 11 cardstock, which is another plus.
Another tip that might help: search for scrapbook sketches online. They will help you put together a layout more quickly.