Use Those Critical Minutes Before You Speak.
Many speakers use the last few minutes before they step in front of the microphone to do a final run-through of their speech or presentation. This results in the pent-up energy (aka nerves) becoming concentrated to the point where the speaker is a bundle of jittery excitement. They step up to the lectern or onto the stage and it bursts out causing their voice to rise or their pace to speed up.
A better way to use those last few minutes is to first, expend some of that energy, and second, to relax. As you wait, do some physical exercises, nothing dramatic of course, but along the lines of bouncing on your toes, flex your hands, clench your core, or whatever you can to burn off that energy without breaking a sweat. {Some top speakers will tackle a hard workout in the hours before they speak, but only do this if there is time to shower afterwards!} Once you have run through your low-key physical exercises, move to a relaxing practice. Engage in some deep belly breathing while visualizing how well you will speak and how well it will be received. When you step on the stage, you will be calm and in control.