I only have one suggestion, if you get really nervous, don't stand and speak, sit in a comfortable chair and speak. Bar stools are good, as long as you find one easy to get in and out of. You may not have to use it, but it's there if your legs get wobbly, and sometimes, if you start out being able to sit and relax somewhat, you'll find when you do have to get up to point something out, you'll stay up because you're less nervous. If there are no bar stools, use a regular chair, just be sure it's placed in a location where people can see you.