Having done a fair amount of public speaking myself, I've found that the trick that works for me is to memorize and over practice the first minute of what I'm saying. That's when I'm most nervous and still getting a feel for the audience. Having the first minute memorized lets me relax and get comfortable without having to think about every word I'm saying. I'll typically memorize my ending as well to make sure it's strong, and then wing everything in between. That's what works for me.