Such a broad question, but I will hit as much as I can.
First, define your business. What services do you offer and how they are delivered. What sets you apart. The most important thing: mission statement. It’s an absolute must. At any time, if your not sure what to do, your mission statement should be able to guide you to the right decision.
Then spend a lot of time doing market research. You have a timeframe in mind? Triple it, at least. Know your audience, your market, your demographics. Male:female ratio, absolute population within 15 miles, population density, median incomes, age distribution, etc. Talk to people, send out surveys. Do your homework. This may be the end for some.
Then you need to look into legal aspects. DBA. LLC. Liscensing. Tax information for you, employees, and contractors. Waivers, liability, insurance. This is usually the endpoint for most.
Now finances. Building new or buying commericial property? Zoning? Building permits? Employees. Contractors. Equipment. All of the legal things I mentioned. Marketing budget. Operations budget. Maintenance.
Those are only the things off the top of my head… you can also try sba.gov for more small business information.