You should research your subject first and foremost.
If you have a nice selection of information you should get down to writing. A well made speech has a memorable start and a memorable ending while getting the audience hooked on what you say. You can always use some rhetoric gimmicks to achieve that, such as three part lists, puzzles, repetition, rhetorical question, whatever you feel comfortable with, really.
Delivery is another concern. What you really shouldn't do is just to read out your speech, since no matter how well crafted it is, a terrible delivery will ruin it. Practise speaking in front of a mirror, that should help your confidence. It's not a great idea to memorise your speech because if you mix up something you will get stuck, thus making the speech less effective.
So basically once you are ready with the writing your speech, just make some notes of it with the first and the last sentence on, and some key points in between, and with the help of these just improvise.
Best wishes for you.
