If somehow you haven't seen them, go check out Tim Hall's recent series on public speaking tips.
I think he's finally finished, and I've been able to nod my head in agreement with many things he's said. I also learned a few things, for instance when reading thoughts on international speaking - something I haven't done yet (but look forward to).
Even if you never plan on speaking at a conference or anything remotely similar - it's worth a read. And it certainly isn't restricted to Oracle topics.
Definitely a good primer on those considering it.