If you're uncertain, poll some of your friends or post to the blabber list.
If you haven't built this kit before, now would be a good time to order one and try it out.
Price out the kit, including shipping and payment processing (usually around $1-1.50) costs. It's best if everyone can walk out with a working gadget for less than $30 total. Note what tools are needed. HacDC may already have what's needed.
Pick a date and time.
Weekend afternoons are nice because people aren't under pressure to rush from work or get home.
Try to pick a date 4-6 weeks in the future.
Create a page for your event, including registration.
Eventbrite is a classic option. To account for transaction fees, enter your ticket price based on the following formula (assumes PayPal): (final_price + 0.32871) / 0.970275 . The easy route: