First find a good gym with fighters that are actually competing-you can use them as a reference point to where your skills need to be, and train as much as your body will allow you to. After you get comfortable with technique and develop some good conditioning start sparring and express an interest in your coach that you want to compete. Until you develop a good base to work off your trainer won't know what it will take to get you competition ready.
I had a few kickboxing matches, and competed in two NAGA grappling tournaments before I competed in mma. They are all completely different animals but they definitely helped with my confidence and first time jitters weren't as bad when I got in the cage for the first time. I would recommend an amateur kickboxing match, you wear shin guards and head gear, and you get a feel for what it's like when the other guy is actually trying to hurt/finish you.
"Danga da danga da dang"- Bas Rutten