"Well begun is half done" applies for the topic in question as well. A friendly smile and upright posture, along with a decent and comfortable clothing would not only make the speaker look approachable and pleasant, but would also help him/her to stay casual. How uncool, would it be to keep adjusting your dress while presenting?
An impromptu session sounds wonderful ! But sadly, not all (incl.me) have the gift of the gab !! Mugging up a speech by-heart wouldn’t help either ! Instead, having a skeleton form of the speach would help. One need not stutter and stammer half way through a session, forgetting the lines. That would only demotivate the person further. Involving the addressees and interacting would also help in making the whole thing lively. The latent advantage being that one could rest assured that no one falls asleep/or atleast waking up the person who has managed a quick nap.
Add Lustre :
Use the opportunity to showcase your technical brilliance. If a PPT is dismissed as too hi-fi for the group your addressing, an OHP would help. There was a lady coming in for an OHP presentation, who used her cigarette lighter as a paper weight on the OHP sheet, which was prompty reflected on the board, and that was enough fodder for us to gossip on the spot. No wonder I hardly remember even the topic that was dealt with ! Hence try fascinating the audience by your techniques which wouldn’t distract the group.
Know your audience :
The age, qualification and thereby the mindset has to be considered before addressing. The audience expect to hear not all that you know, but all that they want to know. Adding humour and illustrating real life examples would bring life to mundane topics. A person who could correctly balance his content with the necessary vigour, would attract audience even in the absence of the mike. While a person speaking at the top of his voice behind the mike with all possible gesticulations on earth, minus content and conviction would only make the audience sleep!
Never suffer a complex :
The initial few minutes are vital. The sneering faces of the audience might not be welcoming, but there lies the challenge ! Once your put off, they win and you succumb ! If your confident enough in the delivery, there is no looking back. Also, a quick collection of audiences’ opinion before starting off would give a clue of what they expect from the session/speech. If there’s absolute silence when you ask for suggestions. be prepared, you are an uninvited guest, and that complicates your task. Modulating the voice would help in beating the monotonous and mundane topics too.
Conquer the impediment :
"Fear" can be extremely distressing. Conquering the turmoil within, would unleash the new you. There’s always someone more intelligent, always someone more attractive and always someone catching more attention. But every other person, is attractive and intelligent in someone’s eye. It all depends on the rapport that you’re able to strike and the reach that your speech could have. The Fear of Fear is the biggest Fear of all times - John F Kennedy, while talking about Cuban Crisis - when Russia was loading tons of arms at Havanna.
Speak your mind :
This is one thing which would defeat the necessity of all other technical requirements. A person could just walk in without any paper to refer back, and still hold the audience in awe if he speaks from the bottom of his heart. Going one step further and pouring one’s heart is frivolous, which would be dismissed as nothing but cribbing. When I’m honest I make an impact, when I fabricate the message, I fail to catch attention. This is true & applicable in the case of writing too (with tweeks of course).
Finally, it is your guts that would win.
A note - in my present co. I conducted many programs for fun and leadership, beyond the call of my duty, being in a Senior level, which was to be done by HR (only if there was one such group). It was very effective, and those guys who gained experience, moved on to a better role, within or outside.