The first thing to do is write a business plan. You can find a number of templates online. The plan covers all kinds of things, including:
The concept (a description of the service or product you will be providing);
The resources necessary to run the business (which describes all your one time expenses such as for rental of space, and ongoing expenses such as electricity);
A description of the capabilities of the principals; ...
Well here’s a sample table of contents (from here):
I. Table of Contents 3
II. Executive Summary 4
III. General Company Description 5
IV. Products and Services 6
V. Marketing Plan 7
VI. Operational Plan 16
VII. Management and Organization 21
VIII. Personal Financial Statement 22
IX. Startup Expenses and Capitalization 23
X. Financial Plan 24
XI. Appendices 27
XII. Refining the Plan 28
If you use a template, then it kind of forces you to think through all these things, which makes your concept much more viable.