"The very basics"
"As their name indicates, ATC are collectables, a brilliant idea born of the older sports-themed trading cards. The one rule that makes an ATC derives from this: the dimensions of the ATC must be 2.5"x3.5", or 64x89mm.
To this rule are appended a couple of conventions. First, an ATC mustn't be sold, only exchanged, as the whole essence of these tiny works of art is about artists meeting (by correspondence or online if need be) and exchanging their works, thus meeting many artists and getting exposed to many personal styles.
Second, on the back of each ATC the artist writes part or all of the following information: name, contact information, title of the ATC and number (1/8, 2/8...) if it's part of an edition. By definition ATCs are made in limited numbers, often no more than one of a kind. Unique ATCs are called originals; sets of identical ATCs are called editions and are numbered; sets of ATCs that are based on one theme but that are different are called series. Don't be intimidated by the concept of small editions or originals: very few people are anal about this. What most collectors really want are cards that were made with care. Based on that, numbers are meaningless.
That's all! The above is all you need to know to start making your own ATCs. Common sense dictates that they should be sturdy enough to survive mailing, and of reasonable thickness (unless you specifically want them otherwise. Transparent card sleeves are useful to protect the cards if need be. This is particularly true if they can easily get smudged or if the medium might stick during transport."
This is an ATC that I did for a PAO swap. Rules: use at least one Tim Holtz product. This one is actually my ATC and a little different than the one's I swapped. I used TH papers, TH paper tape, and pan pastels for color. It was a 9 for 9 swap, so I sent 9 and will receive 9 little works of art from my friends. Now how cool is that? I love participating in ATC swaps. It is a chance to send/receive to/from my artistic friends. I have them displayed in a 3 ring notebook placed in plastic trading card holders.