I've found that when preparing for a presentation, writing out my entire speech (in spoken language), and rehearsing from that, THEN boiling it down to keywords

I've found that when preparing for a presentation, writing out my entire speech (in spoken language), and rehearsing from that, THEN boiling it down to keywords on index cards, helps tremendously in organizing your thoughts, determining the level of details needed etc. But this has probably more to do with speech technique than keeping your nerves under control. Once you're on stage, locate a few spots in the back of the room - not cameras, not persons, and keep your eyes at them. Don't look at people, it's confusing at best.