Try rehearsing your presentation I front of a few friends or family, if you adlib you will find its to short, remember to keep eye contact, and if using presentation aids, over head projectors etc, make sure you stay facing the people your talking to, at the start try laying out what your going to do, ie, hello every one my name is ....., I will be doing a presentaion on ........, I will first like to tell you about x then I will talk about y and I will then like to go over z, and there will be time for any questions you may have at the end.
Try to keep it informative and interesting, if using facts and figures, make sure you know the sorce of the info, as your audience may ask where your info is from, if you get asked a question you don't know say something like " thanks a good question, but I unsure of the exact answer, I will find out for you and give you a ring tomorrow morning"
Don't constantly read from notes, as your audance will soon get board.
If you give out hand outs, make sure they have no more than 5 or 6 points on them, as if they are crammed with information, people will just stop reading them
If you mentally dry up, just try asking the audiance what there opinion is on your last point.
Try to think of any questions you may be asked, so that your prepared, if you practice with friends or family make note of the questions they ask, get them to give you honest feedback.
If you are worried about speaking in public, go to a public place and do your presentation in front of your family and friends there a park or mac Donald's would do, you will feel a bit silly, but if you can do it your feel great, and it will make the real thing seem easy.
Good luck and let us know how you get on.