Thats a very vast question so I shall provide a very vast answer.
Change the way you view yourself. If you are wondering how to become professional then you feel as though you are not, because you are seeking for something. We only ask the questions for knowledge that we have not yet obtained. What you believe to be professional is all up to your perception and how you view "professional" internet marketers.
Is it the way they dress?
Is it the way they act?
Is it their money?
If money is what makes someone a professional, I know a ton of professional school teachers that make less money then I made as a waiter. So is it really the money? No.
It's your perception of what professional is. So if you view yourself as a professional, and you start walking the path of a professional, and moving towards becoming a professional, then that would ultimately make you a professional wouldn't it? You could be a professional content writer on the web and not make shit. Although if you are marketing your skills on the internet, wouldn't that make you an Internet marketer?
So to be a professional internet marketer takes a willingness to never quit learning at the root of everything.