Once you have the basic idea of what you want to present, you have to get it accepted by groups and get the opportunity to show it. Your best line of strategy is to start off giving your intended presentation to a local LUG and let them critique it. Audience feedback is cruicial, especially if you have not done a presentation before.
So what's the secret for talking to a LUG? In many cases, just offer. LUGs like to have speakers for each meeting to give a reason to get together other than go for a beer after the meeting.
In terms of conferences that you would like to attend, check the major
conferences and expos out there. Many are listed at Linux web sites,
some send out a call for papers (CFP) to approprate discussion lists,
like <discuss@linuxdoc.org>. Many will have
either an e-mail CFP, or have you fill out a web form.
I cannot comment on what papers are accepted or declined, mostly because I don't know how it works. The best I can say is to see what topics have been selected in the past and tailor your abstract that way.
Assuming your presentation has been selected, try and get some information about the location, dates, time, and so on. This will have a lot of bearing on how your presentation is laid out. A presentaton using printed slides will appear different on screen than one with an LCD projector that connects to your laptop. In some cases, you will need to bring your own laptop to the presentation.