Speaking in front of an audience is more effective if you are teaching people how to do something.
Many people will stay focused and attentive if you are sharing your experience and involving them in the learning process.
Here are some ways to be successful with your public speaking by using teaching techniques.

• Get everyone involved right away.
  Assign audience members a job, and then get them excited by telling them what they will be able to do by the time you finish speaking.
  
• Prepare a handout for them that requires participation on their part.
  You may want to include fill in the blanks or even a couple of short answer questions on this handout.
  
• Hold a contest and collect their business cards to choose a winner.
  This way you will have everyone's contact information and can ask for their permission to add them to your email and regular mailing list.
  
• Have a theme that runs through your speech.
  This will make your public speaking much more interesting and help keep the audience awake and focused on what you are saying.
  
• Have people hold their questions until you get to a specific point in your speech.
  This will help you to keep control of your audience while you are speaking.
  
• Have several people from the audience help you to pass out your handouts and to collect the business cards.
  This will free you up to speak to the group and hit all of your salient points.
  
• Practice your public speaking several times before you give a speech in front of an audience.
  This will help you to know your material better and keep you from being so nervous.
  

These 7 tips will make you a more effective speaker.
It is also a good idea to learn from someone who speaks professionally for a living.