We got lucky with ours. I met a local BYC'er who lives in my same city at the time when she was just getting chickens and we'd had ours for almost a year. As coincidence would have it, a lady at her work quit selling eggs, so we just slid right in and took over. We average anywhere from 3-6 dozen per week in orders. Our best layers are the sex links, barred rocks, and RIR's. Forget the buff orpingtons. They are nice birds but not predictable layers when you need them. We collect and I drop off to her each week and she delivers them at work.
We started into ducks and had a ton of eggs. The regular chicken egg customers prefer to stick to their chicken eggs, so I had to resort to putting an ad on Craig's List. It definitely paid off and we are selling upwards of 10 dozen duck eggs a week. I had a customer drive an hour each way today to pick up 4 dozen.
Best advice I can give you is to advertise however you can. A sign in the yard works good but only if you're home (which I am not). Craig's List is amazing as is word of mouth. I only have one neighbor who buys two dozen maybe once a month, if that. If you can post a sign at your local feedstore, that helps too. It takes a while to get established, but patience pays off.