What tips and piece of advice will you give on growing a product that involves two parties ?

Let's say I want to build and grow a freelancing platform, which involves two parties, a buyer and a freelancer. To attract freelancers on the platform, I will need to have buyers on the website and vice versa. What's the approach that these type of platforms/startups take to grow initially ? It will be helpful for community if you'll share your experiences, tips and advice.