It’s hard to find an excerpt from this remarkable post, so I’ll just capture the conclusion here and urge you to take a look at How to Prep for a Presentation.
I’m sure you’ve heard it before, but I’ll spell it out for you: Fewer things generate a higher return on investment for time spent than giving a great talk. Fewer things are more disrespectful than having that kind of opportunity, squandering it, and wasting a room full of people’s valuable time because you didn’t prep properly. So when you get an invitation to speak, be of service. The doors that will open to you because you gave a great talk are plentiful. I’ve used this technique for everything from my talks on the Information Diet, to Best Man toasts. It never fails. I hope it’s useful for you, too.
There’s a treasure house of information for speakers here (and more than enough to fuel my feelings of inadequacy and guilt).