Always have business cards with you, especially at a conference, workshop, or convention. You'll be giving them out to agents, editors, other authors, fans, attendees, conference organizers, speakers, and more.
Most people give out standard cards. Some make fancier ones, like tent cards that when folded are the same size as a regular card (or even larger). Typically, the tent cards have the title, author's name, and a graphic on the front, a blurb about the book on the inside, and contact information on the back.
You can have business cards or tent cards made up at a copy shop. They're not terribly expensive, but you usually have to print a ton of them. If you don't want 500 or 1000 of the same card, you can make your own. If you have a computer and printer, they're easy to do.
I do have a couple of standard cards that I keep in my purse or pocket. One is for work--it lists my name, address, email, and business info (Director of Women's Marketing, Legends in Our Own Minds, LLC). If I'm speaking at a conference or event, I might take cards that on the back have information about my newsletter, Doing It Write!, and how to subscribe.
For your “writing” card, the one that gives out contact information, you could consider printing the back side with the title and logline for the manuscript you’re pitching at the time. Since this card is the one most likely to change, it’s the one you might want to do on your own in smaller numbers instead of two hundred or a thousand at a professional print shop.
When you go to a conference, keep the cards handy. Don't bury them in your purse or book bag. Have them ready to whip out and give away. And take cards from others. After you leave that person, make a note on the back to remind you who that contact was or why you have the card. You'll be surprised by how quickly you forget when you go back through 20 cards you collected during the conference.
Your business card is a tool. You can use it to network, to market yourself, to advertise your most current book and the ordering information, to make contacts. It can be one-sided, folded, two-sided, fancy, plain, with graphics or text only, black and white, colors, white-background or a texture. Whatever fits you and whatever you're promoting.
To misquote Nike: Just Use It.
5 months ago