Three years ago I came up with the idea of creating Character Trading Cards as an alternative to the usual character info worksheet. I also thought it might be a fun way for authors to promote their work.
It seems the idea has resurfaced, as folks have been asking me for links, so I've unearth the old posts from the PBW archive vault and checked to see what's still working.
The free online generator I used to make my first example is still working nicely, as does another free card generator over at Read Write Think. We also had another pretty neat discussion here with lots of ideas from everyone about using trading cards as promo.
When I made my first card (you can see the full size original here) I wanted to use it mainly as a personal/quick character reference, so I listed things like Lucan's talent and scent. When you make cards for yourself, you'll want to jot down the most important facts you'll need for writing purposes.
A card you intend to use for promotional purposes should have things like the novel title and a teaser, like this one I made up today for Nightshine at the top of the post. On both cards I used cropped cover art images that depict the characters, but you could probably tweak the card to show an image of the entire novel cover.
Other ways you can use trading cards as promotional items: design one for your blog or web site that shows the URL, an avatar or graphic associated with your site, and a brief description of your content. If you're a Twitter or a Facebooker, add on those contact URLs. Series authors, you could probably fit thumbnails of your covers and titles in reading order on your cards. Cards for upcoming releases could include the date they hit the shelf and ISBNs.
If you want to make your trading card about you, I'd put your bio photo or a business graphic on the card, all your contact info and a tag line that describes what you do, i.e. "freelance editor" "cover art designer" "romance author" etc. A trading card could probably be scaled down to the size of a business card, although you'll have to watch the quality of the graphics and font size, and see if it's still readable when you print it out.
For printing purposes you'll want to use cardstock or a decent weight photo-quality paper. I remember that I did experiment with printing mine out on scrapbooking paper, printing on the white side so the print side would be the backing, but the results weren't that great and the card was too flimsy. Scrapbooking papers may have improved so you might see what's available at your local craft shop. If you're planning to produce a large quantity of a single design it may be cheaper to have them professionally printed.
Back when I originally proposed the idea authors Shiloh Walker and Sasha White actually ran with it and did amazing things with trading cards for their characters and novels. My old links to their examples aren't working, but I believe both authors printed and used the cards as real promo items, so they'd probably have some good advice.