There are a lot of sites with useful advice out there. This post is intended to collect several links for future reference.
Technically Speaking – Videos of math research students presenting their findings. I love the examples of bad style along with good style. This comes out of an NSF-funded project.
Joe Gallian’s Advice on Giving a Good PowerPoint Presentation from his article in Math Horizons.
Giving a Conference Talk by Mike Dahlin.
Oral Presentation Advice by Mark D. Hill, includes “How to Give a Bad Talk” by David A. Patterson.
Giving an Academic Talk by Jonathan Shewchuk.
I also have several resources on good mathematical writing that I’ll share later.
Serre’s “How to write mathematics badly” is not quite on topic, but should be included too. It’s easy to find on-line but is unfortunately very quiet.