When public speaking the person should have a clear understanding of his or her audience. This allows the speaker to tailor jokes, references, vocabulary, and etc. to meet the needs and expectations of the audience. The speaker should know the material that he or she wants to cover, but try to avoid memorizing the material word for word. This eliminates the awkward silence when searching for the specific word or words that have been forgotten. Memorize the big ideas. Practice enough that you are relaxed and assured in front of your audience. Eye contact is always a must, but if you’re are shy, look slightly to the left or right of an audience member’s eyes. Grab the audience’s attention with a joke, anecdote, question, or etc., but only ask a question if you are then going to guide your audience subtly to an answer. Keep it simple starting with your weakest points and ending with your strongest. These should be enough to get you well on your way to a successful public speaking engagement.
The previous posts did a very nice job of expressing areas of improvement in public speaking. I would like to take a page out of President Obama's playbook on the topic. One thing I have come to notice about his speeches is that he always develops a certain cadence or structure in his speeches. He has a sense of drama in his speeches that public speakers can do well by in terms of following. He always seems to start off with introductions and expressions of gratitude and then begin his speech with a building up to the critical point. He does not begin with his strongest points, but rather allows the speech to develop these ideas, percolating under the surface. The middle of his speech is where the main points are made, and his conclusions are rousing in terms of being able to end on a note of confirmation or expressing relevancy. Noticing this structure, similar to the one features in dramatic lecture, is something that public speakers can hope to emulate in the delivering of their speeches.
Very good suggestions in mrsmonica's post above. I would add only these. It is important for a speaker to know his material well enough so that he or she can establish eye contact with the audience from time to time, especially when making an important point. Also, the speaker should make very certain ahead of time how to pronounce every word and name in the speech correctly. When a public speaker mispronounces a word or a name, it damages credibility.
Most speakers benefit from slowing down when speaking in public. Adjusting one's vocal pitch lower, especially for a female speaker, is usually an improvement. Learning when to pause for effect, especially when making a humorous or other important point, is a skill that many public speakers need.