It's just one of those things... the more you do it the better you get!
Easier the younger you start, but never too late!
If nervouse to start preperation and practice is the key. I remember when I first started doing public speaking I could barely talk so I use to practice 100's of time's in front of the mirror before. Anything that will build confidence.
If you're at university and it's one with a Debating Society, it's definitely worth joining up- every week I get the chance to hear a great range of eloquent speakers and I often make speeches myself, something I wasn't comfortable with at the beginning of my first year but which now is a lot easier because of the practise I've had. Plus we give each other constructive criticism based not just on the way we've spoken but on the logic we've used and our skills of persuasion. And since we're all friends and go to the pub afterwards, it's a lot of fun, too.
If you're nervous and short-sighted, I always recommend taking your glasses off (assuming you're just standing there and not at risk of wandering off the edge of a stage ) - making everyone blurry helps a lot.
I have to do a presenation on the NHS on Saturday and the student speaking to my group last session said that her friends visualise the audience in their underwear... not sure if that's the best method though!
Confidence is the key - fake it if you aren't feeling it!
I did the Youth Speaks competition at the Rotary and found that speaking up a lot when with acquaintances helped. Try striking up a conversation with people you sort of know but aren't really friends with.