Use Design Thinking principles. Define the "as is" user journey and identify problems/pains. How can you relive those pains and create more gains?

Based on the user needs define the requirements for your solution. Possibly you can create small mockups to visualize your potential solution and show it to users.

Identify the problem that your users really have. How are they solving it today?
What motivates you to solve this problem?

Check if there are any legal implications on your business model. Is the market regulated? What licenses or certificates does it require? Can you avoid them somehow by adjusting your business model, at least for the beginning?

Create a rough financial plan to check if your venture is worth pursuing it.

Develop an understanding of the market mechanism, i.e. who are decision makers, who controls the budget etc.
If possible you can already generate pre-signups or pre-orders. It can be a great way to finance your business or show investors that there is demand.

Take the prototype or whatever you have and start talking to  users about your solution/ hypotheses. Ask open questions and let them use your solution wihout guidance. Identify where they see the most value. Based on that create user segments and select a target group.

Envision how you are going to deliver your solution to clients. Validate your requirements and create more detailed specifications. Start creating prototypes and get them out to users asap. Iterate based on the feedback.

What value do you provide for your users? Do you save them time, money or bring additional benefits?
Create a business plan including market & competitor analysis. Define your USP and how your will deliver that to your clients (4P).
Develop a clear go-to-market strategy.

Decide on the legal form.
Split equity with cofounders and set up a shareholder agreement and the By-Laws.
Apply for necessary licenses and certificates.

Based on your updated financial forecast, derive the net cash flow and run some scenarios for your company valuation. Is it attractive for investors?
Derive financial KPI's and do sanity checks.
How much money do you need to cover your burn rate for the next 12-18 months?
What is the best way to get funding (grants, loans, business partners, equity)?

Craft a compelling sales strategy and find first clients. Conduct a proof of concept to go through the whole (new) user journey with them and learn from the process. Validate your business model and the willingness to pay.

Based on the value proposition, define the USP that resonates with your target group. Use the 4P to make clear how you bring this to the client. Develop Branding/ Corporate Identity guidelines.
Conduct first marketing campaigns and identify the most efficient channels to reach new clients.

Bring your solution (MVP with core functionalities) into a real world environment and collect valuable insights. Based on the learnings, improve the solution.

Protect your IP (i.e. trademarks, patents, etc.).
Set up all legal documents for running your business (i.e. Terms of Use, Partner contracts, Invoices, etc.).

Are you fundraising? Get the necessary documents ready, make it easy for investors to invest.
Find an accountant and consider insurances you need for the business.

Focus on early adopters at first. Implement processes to generate new leads. What reduces the time for user acquisition? How can you activate new clients so that they see the benefits from your product right away? Make sure to retain your existing clients and consider upselling.

Initiate a marketing campaign for your launch. Identify key opinion leaders and partners. Create events and draw awareness to your new solution.
Use various communication channels to bring your USP/messages across. Make sure users can find you (SEO). How do you motivate users to spread the word and launch a referral campaign?

Set up a reliable production environment with the necessary infrastructure.
Optimize the UI/UX.
Define and keep track of KPI's.

Shift your focus towards value creation. Define your value chain and who and what you need. Define key roles within your organisation and evaluate where you need external support (e.g. outsourcing, partnerships).
Set milestones and KPI's that you need to achieve this year (e.g. use the Hoshin Kanri Matrix and OKR's).

Implement an employee stock option plan or a phantom pool.

Now is the time to grow. Secure enough funding to invest in Sales & Marketing.
Find reliable partners for bookkeeping and financial reporting. Integrate processes into your operations and automate where possible.
Incentivice employees, consider 4 areas for time and performance related compensation (base salary, pension, profit shares, company shares).

Include new target segments and get into the mass market. Can you automate the sales process? Improve the customer retention rate and increase the customer lifetime value (LTV).

Would your users hate it if you shut down the business? Make sure you got product market fit before scaling.
While ensuring loyalty and implementing customer retention measure, start growth hacking initiatives. Try a lot and measure the success of campaigns.

Adjust your solution for the main market.
Make sure you have enough capacity to scale fast. Automate processes as much as possible. Can your users completely help themselves without your help?
Track the product usage and other KPI's.

Identify new segments to sell to (i.e. international, new user groups/mass market). Do you need to adapt your offering? How do you get to those new clients and who are key stakeholders in the new market?
Set clear goals and communicate them. Implement effective processes.

Depending on your business strategy (optimization, innovation, exit) find the right legal advisors to execute on your strategy.

Depending on your business strategy (optimization, innovation, exit) find the right financial advisors to execute on your strategy.

Automate as much as possible. Potentially a different sales system is needed.
Create long-term partnerships with high lock in effects and recurring revenues.

Reduce marketing expenses. Keep existing clients and hear their other problems.
Test new solutions and do the whole cycle again.

Optimize the processes for the existing solution and reduce costs as much as possible.
Start developing new solutions and do the whole cycle again.

What is the future of the company: continuation, innovation or exit?
After reaching the top of the S-curve, start on a new growth trajectory, while optimizing the existing business.
Develop an exit strategy if needed.