Start like everyone else does: work out your business plan. Understand exactly what it is your business will be doing, what it will involve, who else (personnel and other companies) it will involve. What resources do you need to begin, and what will you need to actually implement your service/product.
What is your revenue stream and what are your outlaying costs? Will you need to borrow any capital to start with? What will you charge for your service/product, and how long will it take you to earn back and pay off your borrowing?
You will also need to consider regulation and legislation: how much of it is there, what applies to you, will you need to register with a professional or national body, do you need certification, do you need permits or licences?
What stage is your offering at: is this just an outline of an idea, of do you have a proof of concept? How much will it cost to prototype or test this concept?
How and to whom will you market this offering? What are it's USP's? Can you back-up your claims for it with data and evidence? Have you done the research to show there is a space for your offering?