It's a painful to get started with, but I can testify that Michael Hyatt has got it right again with this suggestion:
Before you give a speech, practice it out loud, on your feet, as though you were in front of a live audience.
He then gives seven steps to make that practice most effective, and personally I find this one most pertinent when starting out practising this way:
4. Stand up and give your speech out loud. This also makes a difference. Your physical posture affects your energy level and overall confidence. I put my outline on a podium, countertop, or desktop, and then moved around as though I am presenting in front of a live audience. It’s also helpful to me to visualize two or three people I am speaking to in the practice audience.