(speaking as someone who literally gave buttloads of presentations all over the world for over a decade) if you use slides i suggest reading cliff atkinson's blog "beyond powerpoint bullets". in it he lays out ideas, principles and templates for PPTs (and any other preso tools) that tell stories. these are based on cognitive studies, like the number of bullet points you should use based on how much your audience can…
I'm curious, how did you et into the 'speaking business'? It seems a lot of these conferences only invite people to speak who have already spoken at large conferences. I did a talk at a local usergroup (5 people attended) and I loved it. I want to give talks at bigger conferences, but my proposals always get rejected. It seems once the ball is rolling, it just keeps rolling. Got any advice?
"Your submission will be judged by your ability to communicate succinctly in writing, how good we think the talk sounds, what other people say about you behind your back and whether, frankly, we feel like people are going to be happy they paid money to see you yap for an hour."
It sounds a little harsh, but I think it's true. Getting to know people involved in the community or conference organization will pay off.
It's a big leap to go from a short user group presentation to hundreds of people listening to you for an hour. So you should expect to spend time getting to know people and money on attending other events in order to get there.
Of course, if you have a truly awesome new idea that nobody else has thought of, you can skip that step, but very few people do.