Define your problem statement. It is good to use design thinking methodology, doing user and market research. Your problem must be big enough / real problem that you need to solve so it can translate to the service / product that you are offering.
Identify your solution, develop and test it using MVP method to make sure that you can pivot when necessary
Build your business plan
This is where you can understand better what is your cost, how to maximise your revenue and ready to enter the market