Last week, President Obama made an unforced error, mispronouncing a word three times in a public speech. Public speakers of all types risk this sort of thing by not practicing.
Practice, which I define as simulating the real thing, makes performance second-nature. Have a colleague watch you give your next presentation. Hire a coach to walk you through your speech. Do anything that lets you get better before you are on the stage. Don't go into any public appearance without having run through your material. Practice may never 'make perfect,' but it always helps people own their moment.