Sure this has already been covered. But content is king.
A great way to generate content, is by making fake users, and while under those aliases share the content amongst “them” to appear as if you have an new yet active and organic community. The more you do this among yourself, the more content your forum will have, the more it will appear on search engines, and the more traffic you will generate and eventually actual members that aren’t just you.
People will tell you this is frowned upon, and deceitful, that you will probably get exposed and have your reputation tarnished. Whatever, in the real world you got to fake it to make it, just make sure you aren’t an idiot and you always use a different vpn or proxy for every account you use. If you can’t match up the IP’s there is nothing to prove, and thus nothing to expose