My old boss, Mathew Patterson, shares his process for preparing for a talk. He gives details on everything from choosing a topic, to writing the outline, to going through several drafts.
My own process is similar. I tend to start in a text editor (iA Writer on my iPad, Ulysses on my Mac) to capture the main points. The flow of my talk then comes into shape in Keynote. The slides are minimal, but details are included in my speaker’s notes.
The key through the whole process is that you become so familiar with your content that you do not need extensive notes. There is no need to read during your talk. I rarely need the speaker’s notes because each slide is itself a trigger for what I plan to say. When you know your content thoroughly, things can go wrong and you’ll still deliver a good talk.