You need to learn about one of the disciplines that MMA involves first and build a good understanding and background in that I think. Then from there you can continue to focus on just that like some coaches and trainers do or instead expand into those other disciplines and areas and acquire experience in them as well. Going that second route you are easily talking about 12-15 years of experience and background. Just to be well versed in one discipline and training involved for it you are talking 5-7 years of experience and background really.

My answer is based on a number of things including seeing how poorly trained and prepared some of those fighting really are when I am judging them as amateurs. Even an amateur fighter in his first fight has no excuse for not having the basics in stand-up, grappling, wrestling, take-downs and a few basic throws, along with basic chokes and submissions. However I way to often see fighters that don't have those basic aspects in those key areas and its in large part due to inadequate coaching and training rather than the fighter's own desire.

When fighters are then put out there fighting someone who has the benefit of good training and preparation then the differences are usually pretty obvious in those key areas that I mention and it of course results in that poorly trained fighter losing in most cases. Athletic ability and things like speed, physical toughness, and aggressiveness are generally not enough in themselves against a better trained opponent or will only carry you so far.

You can go online and learn all you need to about mma fighting from videos. After that its simple to become a train since its an unregulated field, there is no licensing or anything required.