I just want to say that ATCs are the best way to get over the idea that you aren't artistic! Anything really does go with this art form.
I've seen them made of polymer clay, small sheets of embossed copper, pieces of glass taped around the edges like a stained glass piece, plastic from milk jugs, cardboard, plywood, fabric, burlap, laminated leaves, crochet, knitting, and the list goes on infinitely. In the outer larger world of ATC trading, there are no rules other than the 2.5 x 3.5" dimensions.
I've seen some that have parts attached by brads that you can pivot and unfold to show a person with arms and legs and/or wings, that all fold back up into the 2.5 x 3.5 size. There are little houses that are three-dimensional when unfolded, but they still comply. There are little ATC zines and books that are accordion-folded with many pages, or folded in a certain way to be an 8 page book made form one sheet of paper.
They come with strings and fibers and ribbons and beads and tags and stars and feathers and bones and playing cards, watch parts, optical glass, scrap booking die-cuts, rubber stamps, linoleum prints, woodcuts, etchings, pen and ink drawings, acrylic paintings, oil paintings, pastels, pencils--graphite and colored, watercolors and crayons.
Don't let anything limit you in this terrific art form, let your imagination fly free and make it small!! I particularly like doing a sheet of card stock all over with ink doodling then cut it up, using the ten-card template, into ten cards. Even if you photocopy the whole sheet and turn it upside down, you can get ten different cards off the same design! Then color it, ten more, then cut them into pieces and glue them onto a sheet of colored stock--ten more! And that's just one simple technique!
The ATC-world is your oyster--eat it up!..."