You Can Guarantee Results
You should know how many saleable images you consistently produce in any given session. While people will start asking you to do shoots for them when you've shared a few of your best images, you can't go to a shoot with the hope of creating a handful of keepers. You need to be able to create a gallery, and do it every single time. If you aren't sure you can do that yet, do a few portfolio build shoots, treating them as if they were regular sessions; those results will give you the information you need.
You Have your Paperwork in Order
In addition to your DBA, you need a business bank account, and tax forms, at a minimum. For your own protection you'll also want a client contract and business insurance.
You've Crunched your Numbers
A sustainable business pays you a living wage after expenses and taxes. If you want to keep it easy- assume a third of your fee goes to taxes, a third to business expenses (prints, gear, fees, gallery hosting, props, etc.) and the last third is your wage. All of a sudden, that $300 session (with an hour of planning and client communication, two hours on the shoot, and 7 hours to upload, edit, print, reveal and deliver) costs you 10 hours of work but only earned you $100 in wages... basically minimum wage. Think this through before you make a single sale!
You've Defined Your Services
When you begin selling a service, you must be crystal clear about what you will deliver, and what it will cost both you and the client. How long is a session? How many images will you deliver? Will you be all-inclusive, pay-per-image, or a combo of the two? Will you edit all the images, or only purchased ones? Will you include detail retouching, or charge extra? WIll you help with the session planning, or will clients need to choose their own outfits and locations? Are prints included?
Whatever you decide, communicate it clearly, in writing, before any money changes hands.
You've Set Your Product Line
Unless you only offer your work as digital downloads, you'll need to do some more research and pricing calculations. How much will you charge to burn and deliver a USB? Will you package it, or just hand it over? All these add costs and take time, which, as a business, you have to charge for. Will you offer prints? If so, on what paper? What finish and mounting options? How will you package prints for delivery? How much time will it take you (will you have to do any extra editing if they order a 16x20?)? If you sell albums, from which lab? How many hours of your time goes into design? How many proofs and changes will you include? What if there's an error? Are you prepared to cover costs to reprint an album that cost you over $200 to produce?
Offering boutique printing and design service can set you apart as a high-end studio, but it (like everything) adds a layer of complexity, and expenses you'll need to cover. Make sure you've thought this through prior to your first booking.
Ultimately, your businsess will be a reflection of your vision, but if you want it to last, start with a plan and save yourself some newbie headaches.