The way get started is to quit talking and doing
Once you have a talk idea, it’s time to build the talk. Conference talks are scary, so you’ll want to avoid it. You’ll silently make slides or silently write an outline. These would be great preparations if you were going to stand on stage and perform the act of silently writing notes in a text editor. You’re going to stand on stage and talk, so your preparation should be made up primarily of talking.
Your first step is to choose a topic; we’ll assume that you’ve done that. Find a room where no one can hear you. Stand up and start talking about your topic to no one, projecting your voice rather than mumbling. Wander around a bit. In short: act like you’re on stage.
Every part of this is important. If no one can hear you, then you won’t feel embarrassed to speak freely. If you speak out loud, project your voice, and walk around a bit, then you’ll condition yourself to stand on stage and give a talk. By the time you’re on stage, it’ll be so ingrained that even performance stress won’t stop you. More on that later.
You’ll be tempted to think “this part doesn’t matter; I can do it silently and get the same effect.” You can’t! You can’t learn to play a guitar by writing music, you can’t learn to write by talking, and you can’t learn to give a talk by writing an outline. Every talk is new, so you have to relearn every time. You need to hear the jokes to know whether they’re funny; hear the pace to know whether you’re becoming boring; and hear your confidence (or lack thereof) to tell you when you’re straying into territory that you don’t understand.