First, prepare. Yes, I know there is a website filled with fair-to-good advice that advocates minimal preparation, but this is a bad idea for most speakers. When you really know your material cold you will be able to deliver in a much more natural manner. You won't spend your mental energy on recall, but on expression. When you think you have your points memorized you are ready to start another level of rehearsal. You can reach the stage where your main points are as easy to recall as your name, address, and phone number. This will create confidence for you and release you to began experimenting with your delivery style. What freedom!
The second point is one I haven't seen on websites or in textbooks, but it's a key strategy. Make sure your focus is on your audience. Let's say you are standing up in front of a group to explain to them the importance of a healthy diet. Is it important that you speak flawlessly? The priority is the health of your listeners, right? You have valuable information for them. If wearing a silly hat with carrots and tomatoes all over it would convince them to eat more vegetables wouldn't you do it? So stop worrying about how you are percieved and focus on the needs of your listeners. If you are truly prepared, this change of focus can quickly calm you down. As an untalented, untrained choir member who has had to sing solos in nursing homes before I can vouch for this approach.
Yes, there are other items that will help you overcome your fear of standing up in front of a group, but these two are the most basic, and the best starting point.
