Actors strive to make interesting choices and then commit to them fully. If you decide to be theatrical or to take a risk on the platform, don't hold back. When I beat up my rubber chicken, I strangled it, slammed its poor little head into the podium, threw it to the ground and jumped up and down on top of it, screamed and growled and snorted. Be fully committed to your message and your choices. If the actor's mind is allowed to roam free, it will focus on nervousness.
Actors relax by concentrating on their preparation, the script, and the other actors.
Speakers can relax by concentrating on their drive, the client, the audience, customization details, room mechanics, etc. Marjorie Brody relaxes by meeting and greeting audience members, giving out handouts, and chatting with them before her presentation. Alan Ovson concentrates on his points of wisdom. So I concentrate on re-prioritizing my points. Don't expect to win your Academy Award without effort.