When speaking in front of an audience, you need to remind them of why they are there listening to you.
The best way to do that, is to remind them of their need and then guide them towards a solution.
The best way to establish that need is to remind people of the pain that they are in.
Take a few minutes to outline what you perceive to be their pain point.
Whether it's losing those last 10 lbs, getting that new job or whatever it may be, make sure that you take the time to remind your audience of their pain, and remind the audience that you will be giving them a solution to their pain later on in your speech.
Here are 3 ways that can help you establish or reinforce "need" in your audience,

1. Take a mistakes article (5 biggest mistakes that you can make while...
   ) and use those points to establish the need.
   Just go over an article that you've written that outlines the 5 biggest mistakes that people make in your area of expertise and go over those points.
   
2. Continue building the need for what you're talking about.
   Use statistics if you have them, tell stories that are related to what you're talking about etc.
   Backup your information with as much legitimate information as possible.
   Do not make anything up.
   
3. Help people see themselves committing one of the popular or common mistakes that you're talking about.
   This point may be easier to accomplish in some areas than in others, but you should know your audience enough to be able to tailor your speech and meet your audience where they are.
   

Remember, you need to establish a need during your speech to hold on to your audience's attention.
At the end of the speech, you need to deliver on your promise to give the audience a solution, don't forget that.