How to design an ideal and effective organisational structure for a sole proprietorship firm?

Hi, I want to design an ideal and effective organisational structure for a sole proprietorship firm.
The details are as follows:
1. No of employees 40
2. Branches 2
3. Departments 10
4. Business marketing services
5. Area of operations Maharashtra
Please guide me as how to begin with? What factors should I keep in mind?
Thanks in advance

You may better go for a flat structure now. With branch heads at the respective locations as head of operations in the respective geographical areas and reporting to the sole proprietor. The sales force could be assigned specific territories and made to report Branch Head.
The organisational Structure is never static, it has to evolve as the organisational activities expand. As it grows further you may have a Matrix Structure. There will be functional differentiation into different departments (like Marketing, Sales, After Sales Service, Finance, HR & Admin etc) at the central level and geographical branches at the working level. So the Sales executive directly dealing with the customer will have two reporting relationships, like administrative reporting to the geographical head and functional reporting to the Head of the Department.
More study of your operations is needed to advise further.