Want to avoid choking? Take Inderal. It's that simple. For activities like public speaking and auditions, it's literally a magic pill.
Another approach is Don Greene's. He used to work with olympic divers, and now works with classical musicians. My ex took his class in college, and she eradicated all of her issues with nerves.
Edit: I am not a doctor, this is not medical advice.
Timothy Galley's Inner Game Of Tennis seems relevant for non-anxiety/mild-anxiety based performance issues. He believes that over-analysis and self criticism prevent both learning and peak performance.
I have a problem with anxiety and for me the only way I can really combat it in these situations is to feel over-prepared, take deep breaths, and try not to talk too fast. Also, keeping a few portable face wipes helps (in case I sweat), but usually just having them on me is reassuring.
Another approach is Don Greene's. He used to work with olympic divers, and now works with classical musicians. My ex took his class in college, and she eradicated all of her issues with nerves.
Edit: I am not a doctor, this is not medical advice.