We asked the speakers of TEDxValencia the following: imagine that after the event a person asks one of the attendees of the event what your talk was about. What should this attendee remember from your talk? What should he transmit to the other person? That is the objective of your talk.
Chris Anderson, the CEO of TED, says that the number one problem of speakers at TED events, in their first draft, is that they want to tell too many things.
The biggest problem I see in first drafts of presentations is that they try to cover too much ground. You can’t summarize an entire career in a single talk. If you try to cram in everything you know, you won’t have time to include key details, and your talk will disappear into abstract language that may make sense if your listeners are familiar with the subject matter but will be completely opaque if they’re new to it. You need specific examples to flesh out your ideas. So limit the scope of your talk to that which can be explained, and brought to life with examples, in the available time.
You can find more information in the article “How to give a killer presentation“. A clear objective helps you to limit the scope of your talk.
An example of a talk with a clear objective and full of examples, anecdotes and references is: The game that can give you 10 extra years of life.