Maybe you need some help from a trade association that provide education and assistance to people forming trade associations.
Sorry, couldn't resist that.
Well, if I was going to do it, here's the steps I would take.
1 - Determine if there were any laws or regulations regarding associations. The Secretay of State's office can probably tell you that.
2 - Decide if I wanted to be non-profit (tax exempt) or profit. The IRS has resources on its website for non-profit (tax exempt) associations.
3 - Incorporate.
4 - Buy association liability insurance.
5 - Seek paying members.
However, since there are thousands of trade associations that exist to serve almost any kind of business out there, I think I'd want to line up enough preliminary membership commitments to make it worth spending the couple of thousand that it would take to get started.