Welcome!
The first thing you need is a good teacher. You can look in the directory here on ballroomdancers.com , and you could also tell us where you are and perhaps some people can make suggestions.
The next thing you'll need is a partner. Some people dance with their teachers, some dance with a peer. There are trade-offs no matter which way you go. If you are young (under 25) then I think it's better from a competition standpoint to find a peer to dance with. A good teacher can sometimes help with that.
I started out taking lessons and dancing in competitions with my teacher. I did this until I got comfortable with what I was doing, and then I started looking for another amateur near my age and level to compete with. Partner-hunting can be very frustrating, and in your first few partnerships you'll most likely end up dancing with someone who isn't exactly right but who at least is available and willing to give it a try. It took me six yeas of looking to find my current partner. During the time I was looking I danced with several different partners -- all good guys but who just weren't right due to height, body type, availability for practice and lessons, or other such factors. But I still learned a lot from each partnership, so each one was an important part of my overall dance training.
