I once heard that Steve Jobs' 10,000 hours rule - it takes someone 10,000 to get really good at a task - applied to his own public speaking. He simply wrote his speech, and then practised it again and again until it was right. Perhaps charisma CAN be acquired.
So, I sat down to write my elevator pitch, aiming for 60 seconds. How to get my key messages across briefly? Having read it through and tweaked it a few times, it's down to 55 seconds.
Always keep in mind the attention span and level of interest of your reader or listener. Keep It Simple, Stupid.