starting with bday parties! advice?

Did anyone start out by painting at bday parties? Any advice for a newbie? Do you make them pay upfront? Do you have a contract or is it all verbal? How did you find your bday party gigs? Also how many designs do you typically paint in a party? (All different or go with a few standards to start?)

I would like to start booking some parties for Spring so I am trying to get this going now! First I need to work on getting some photos! I am making a blog (with photos) I have a URL already and cards made up and then I will just need to create a photo book to take with me..a menu board type thing is over the top for a bday party right?

Anyway, any advice would be appreciate. (Or even just what NOT to do!)

I set up my birthday party rates based on the number of faces I am to paint.
Small party---up to 10 faces, Med Party--up to 20 faces, and Large Party--up to 30 faces. Then there is a "per face" price for any face over the party limit.
If they do not know hoe many will be in attendance, then it falls back to my set hourly rate and is up to them to hire me for enough time for their event.
This allows me to set the party rates at a slight discount over the hourly rate.....so then it is considered a "package rate".
When I get an inquiry and they want to book, I send out a invoice/contract. They then have to read, sign, and return the contract portion to me with their non-refundable retainer (deposit that is usually about half of the total.....$50 minimum though). When that check clears the bank, then they are confirmed on my calendar for their specified date and time. The remainder of the balance is due at the event.
The retainer is non-refundable, but can be put toward a future event if they have to cancel.....provided that they follow the proper cancellation procedure that is laid out in the contract.

I'm just getting started with the birthday party gigs as well but I've done a few now and have several more booked. I sent out postcards to all the local businesses, day cares, restaurants, etc. and the people who have contacted me have actually been the people who work at those places. Evidently they've posted the postcards on the employee bulletin boards. Another way I've gotten bookings is from a craigslist ad I've kept up now (about to post my 3rd). After you get the first few, word of mouth helps book most of them after that!
I have them pay a $25 deposit through the website (most pay by paypal but since I can take credit cards through my regular business some pay that way as well). I have party packages listed on my website, but still have to make adjustments to those once in a while since I'm just getting started and you can never anticipate every kind of call you might get!