This is such a deep question that reqires such a long, detailed answer, depending on your situation. It all depends on where you are in life - have you already attended school? If not, there are some schools that offer event planning degrees. If you've already finished college, then it's not worth going back - experience is much more important in this industry than schooling.
I recommend going to this website: www.careers-in-event-planning.com, and click on the "Career Planning" page. It helped to guide me in the right direction; also I started out by volunteering for local events, and that helps get experience (the website talks about that too).
It seems like a long process, but I've been in events now for three years and it is so worth it! There's no short cut to success, I guess!