I will launch a start-up with a couple of friends. We will work as data science and data engineering consultancy. All of us have similar backgrounds in maths, physics, and electrical engineering. How to find clients? How to build a network? I have some personal contacts, but that is not enough.
The short answer is - build media presence. You should probably start with building a website in which you describe what you do, why you are good at it and why should the client choose you over your competitors. You have to build an online presence(FB,IG etc..).The site and all your profiles should be optimized. You will need good SEO in order to get those clients to your site and all the digital marketing tools to track your progress.