You can never expect your presentation to be perfect without any practice. Nobody is a professional, everyone needs to practice, to be an expert. The best way to practice is to time yourself. By doing that you can see whether you are talking too fast to finish on time. Or whether you are talking more than it requires and wasting precious time.
Another way to improve your presentation skills is to practice in front of someone. Ask someone, a friend, or someone from your family to stand in front of you. Later, deliver your presentation in front of him/her. But, if you are the kind of person who is shy to deliver in front of someone. Then you should try doing it in front of the mirror, it will help you in the same manner.