I was asked to speak at a Burns supper about three or four years ago. It went quite well and I now get asked to "do a turn" on a more regular basis.
I attend a few Burns, St Andrews and other functions and I hear many speakers. Some of these are excellent, others are mind blowingly boring. I watch them all closely and think about what they are doing right and wrong and try to apply this to my own speeches.
I believe that experience is the thing. The more you do it the more comfortable you will become. Obviously you also need to know your subject but the most important thing is to inject humour into your speech. People like to be entertained as well as being informed.