Looking towards being a conference presenter in the future
Joanne’s and Kurt’s answers are excellent. You have to be able to clearly and completely describe why your level of expertise and knowledge in the topic(s) you want to present are unique and scientifically sound. Prepare a demo of your presentation(s).
If possible, attend as many conferences/conventions as you can to learn from those who are presenting. The IDEA World Fitness Convention (July, 2012). would be a good start.
Take care.