Practice the words in your head over and over again. Pretend that you are there, in front of the audience. I also mentioned practicing before other people. This is good, but if you are alone, the mirror or even your dog can be a great idea. If you are in a field where public speaking is required, you might want to consider taking a class in effective speaking at your local college.
Many times there are night courses that can really help a speaker to relax at the podium.
These classes are usually small, allowing all of the students to develop a relationship. This helps to relax everyone, which makes for a very nice atmosphere to share, communicate, and learn. The best advice is to be prepared, but even the most prepared person sometimes loses his or her place. If this happens, glance down at your cards. Look for the bright color of the next topic, and move on.