Get your practice's administrative and logistical systems in place.
Prefer paper?
Set up accounting workflow
Hiring
If you have employees: set up payroll
Open a checking account for your business
Apply for a business credit card
Update your contact info with everyone!
Once you've found a physicial location (see "Location") and set up your email hosting (see "Website"), tell people your new information! Update nearby hospitals and private practices, the DEA, state pharmacy board, state licensing office, city business licensing office, local labs and radiology centers, and anyone else in the medical community who knows you. You don't want referred patients or requisitioned lab results ending up at your old employer's office instead of your own.
This is also a great way to start a conversation with other doctors about DPC.