How to grow a forum site?

Hey guys,

I am working on a forum, called MakeMoney.

My question is simple yet complicated:

How do I grow it?

I know that there is some PR you can do, like reaching out on twitter, indiehackers, etc.

But it seems, that this is not enough.

What would you do, if you had to grow a new network or public forum?

Thanks for your valuable insights,