There are a number of traits that dynamic speakers have in common, all of which culminate in one specific attribute.
Please note that not all 'professional' speakers are great in their delivery skills so I am not talking about everyone who makes a high salary on the public speaking circuit.
There are many, many dynamic speakers who are not being paid to speak professionally.

• Making eye contact.
  Good speakers will scan the room and make eye contact with their audience.
  Staring at an object or the wall or being glued to your PowerPoint presentation is not making eye contact.
  This is known as the social component.
  
• Speaking with color.
  Expressing emotion in talking is extremely important if you want to keep your listeners' attention.
  If your delivery is characterized by a monotone voice, it is a guarantee your audience will either fall asleep or start checking their iPhones.
  I refer to this as the emotional component and it also incorporates the use of facial expression and body language.
  
• Knowing your material.
  If you do not know what you are going to say - both inside and out - you have no business addressing an audience.
  Without preparation, there is every likelihood that your delivery will be marred by flaws.
  A mistake or two is not the issue.
  Lots of mistakes due to lack of practice, however, is unacceptable.
  This, the intellectual component, is a priority.
  
• Breathing.
  One of the great mistakes a novice (and even some professionals) will make is to forget to breathe in which the pitch of the voice will rise and his/her speed will get faster and faster.
  Supplementing your air supply is the answer.
  What this means is that you should interrupt your sentences to take a breath - to pause - just as you do when talking to friends or family.
  Do not underestimate the physical component of speaking.
  Without air, there is no voice.
  
• Believing in yourself.
  Approaching your audience with the desire and the intention of doing the best job possible is of utmost importance because if you do not believe in yourself, why should anyone else? Your goal is not to seek perfection but instead to strive for excellence.
  The spiritual component is as important as the other 4.
  

While I have just listed the 5 characteristics of dynamic public speaking, the number one component that all good speakers have in common is that they treat their audience as if they were having a conversation in their living room.
If you can implement this style of speaking into your next presentation, I guarantee that you will not only feel more relaxed but your audience will be impressed with your presentation skills.
Learn to talk to your audience, not at them!