As I've mentioned a couple times previously I teach a free 'how to be a speaker' course, mainly to encourage those that want to speak at our local user group to take that next step. We focus on a lot of the mechanics and less on true public speaking items, and we emphasize practice. One of the things that we've seen from the classes we've done so far is that practicing alone or even with a spouse is not enough, speakers really need time in a room similar in size/layout to the actual room to be used, they need a projector, and they need a critic.
Part of it is just mechanical. When using a laptop you need to know how to toggle the display to run on laptop and projector, or if using the Powerpoint presenter mode how to get that going - and sometimes the laptop/projector don't want to play nice. Getting in a little practice helps build a comfort level (but no guarantees). Practicing at home isn't the same because you need a room big enough that you have to work on your voice projection, and one big enough that you can move around if that's your preferred style.
But the real learning comes from having a critique, the sharper the better. My friend & co-worker Chris recently was preparing for a presentation at the Orlando Code Camp and he picked a topic that contained some items that were relatively easy to explain, and some that are pretty hard for most developers to grasp in 30 minutes. In addition to a lot of practice at home he ran through his presentation three times here at the office while I critiqued, using both my speaker evaluation form and just trying to follow the concepts he was explaining. It was very interesting to watch how much the presentation improved as he made tons of notes about things that didn't work, ways to alter slides to better convey the ideas being presented, and of course his confidence level. I'm not about to take credit for his presentation; he did the work, and he listened to a lot of comments and decided which ones he though would help him improve. I think most people are reluctant to criticize, and tend to fall into 'listener' mode rather than really evaluating - and that just doesn't help someone trying to practice. Criticizing isn't throwing rocks, it's offering insight that the other person really needs. Something to think about the next time someone asks you to sit through a presentation while they practice!
As for Chris, I'll let you read his blog post on That was MUCH Better to see his thoughts on the final presentation.