I was thinking, to begin with, I'll just target kids parties. See what happens from there.
If you want to target kids parties there are several things you'll need to be sure you have straight before you get started. First of all, this is a competitive market everywhere, so make sure you have a great show that'll stand up to any other entertainers in your area. You'll need to find out what the going rate for a kids birthday party show is in your area and set your prices similar (You don't want to undercut the market...OR yourself).
there are several advertising avenues you can take. 1st thing you should do is take out an ad in the yellow pages. Many people grab the phone book first when looking for a local entertainer. It shouldn't cost too much at all to do this, and it'll be well worth it in the long run.
Another great option is to take out an ad out in family magazines and party planning magazines. If you go to your closest party store such as "Party City" or "Party Zone", you'll be able to find the magazines you should check into.
Get out and perform! See if you can't get involved doing walk-around magic/balloons at festivals. Try to perform mostly for kids and when you're finished, hand your card to the parents! (Be sure to have the word "Birthday" somewhere on your business card!) Things like this are great forms of exposure, and a great way to allow parents/potential clients a way to visually see your work!
MOST IMPORTANT!!!! ...Make a WEBSITE! It'll cost you about $50-$80 per year, but you can make TWICE that in one show...believe me, it's well worth it...especially since EVERYONE is hooked up to the internet. Attach key words to your website search such as "Birthday magician" "Magic Show", "[insert your town here]", "party entertainment", etc so that people who search these things will be directed to your webpage. Be sure to include plenty of pictures and clear descriptions of the services you have to offer!
NOW, you mentioned getting business cards printed up. I highly recommend a company named "Got Print"http://gotprint.net/g/welcome.do
I use them to print my business cards, and postcards that I send out for advertising. Their quality is AMAZING...with the uv coating the cards are glossy, and waterproof! People are impressed with a nice card. The company is very reasonably priced as well; a box of 1000 cards, color on both sides, with UV coating will run you about $35-$40. Check it out!