I recently attended some public speaking skill workshops from a senior communications VP of a Boston-area hospital, with extensive experience doing this in crisis situations (eg Marathon bombing). Some of the most pertinent tips:
Memorize memorize memorize. I noticed during her entire talk she never once uttered an "uh", "uhmm", awkward pause, nothing. Nor did she quickly rush through as if trying to recite it before she forgot something. The entire talk flowed naturally, as if she was having a relaxed conversation with you. The best way to do this is to repeatedly practice what you will present. However, a common mistake is trying to go from start to finish over and over again. Break up your talk into chunks and practice/memorize each of those individually.
Confidence and enthusiasm are always key. Think of people with a reputation as charismatic public speakers. Delivery, tone, and body language are as important as the actual words coming out of your mouth. You could be spilling the secrets of quantum physics and the universe but if it's spoken in an unenthusiastic, lethargic monotone, people are gonna go to sleep.
Establish your authority. A common way to do this is to have someone else (preferably an authority figure) introduce you to the audience before you begin speaking. Not only does this save you having to do the whole "Hi I'm blabla from Blabla College and I'm here to talk to you about blabla", it establishes your legitimacy in the audience's eyes. They begin the talk already in the mindset of "Ok, let's see what person has to say" instead of "Let's see if I'm going to bother paying attention".
Know your audience. Who are they? What's their level of understanding? What connection do they have to your content? Should you tailor your message? Avoid jargon?
Anticipate every question. Look at your presentation as if a bunch of snarkish internet neckbeards were going to go over it with a fine tooth comb and pose every difficult or awkward question possible in an attempt to trip you up or expose holes. Be prepared with your answers. But always keep the flow and integrity of your talk paramount. If answering a question would require a long ass interruption, acknowledge the question's validity and offer to discuss it with the asker after you've finished speaking. Always have an exit strategy. There is nothing worse than being bogged down in a line of questioning and losing your train of thought, ESPECIALLY on a topic you weren't expecting to be questioned on.
Develop an outline. The conventional scheme is Opening -> Main body talking points -> Close with a summary. The opening catches the audience's attention. Tell a relevant story, use an anecdote or hypothetical, humor if appropriate, etc. Make it interesting and let them know what they will gain from listening to you. Main body hits the key points. Give details. Avoid slamming people with endless stats and quantitative info. Deploy that selectively to reinforce your points. The conclusion, reiterate and summarize.
PowerPoints = don't overload slides with full sentences. A slide full of a massive text block means they are reading that, not listening to you. Use concise bullets. Don't get cute with excessive fonts, text colors, or animations. Use bold and underline sparingly. For very critical points, reveal them one at a time to concentrate the audience's attention.
Oral and appearance - check on all the elements of your speaking style and positioning. Volume, pace/pauses, tone, inflection, what words you emphasize in a sentence, posture, movement. Be animated but not erratic. Move purposefully, not nervously. Avoid things like bouncing, rocking, pacing, etc. Use the hands and facial expressions naturally. Make relaxed eye contact with multiple people, but don't hold it more than a couple seconds per person. Obviously dress appropriately for the audience.
It can all be boiled down to: look and act like you know what you're talking about and give a shit that your audience listens to you, and practice the hell out of it. Do those two and you're 95% there.