Increasing your speaking skill in public is an achievable goal, especially with a little knowledge of the ways that can help you deliver a great speech with confidence. The suggestions following are simply but very effective.

[edit] Steps

When rehearsing, practice speaking to the room as if the audience were in front of you.
Avoid the temptation to speak in front of a mirror or a video camera (it's distracting) and instead focus your energy on what it feels like to present in the moment.
Practice speaking with your friend(s) or your parents.
Prepare a good plan of speaking. There should be:
- An opening
- 3 good middle points;
- a summary (conclusion)
Don't try to speak on too many issues. In addition, don't wander off the topic.
Think carefully before you talk. Use silence; it can be a great ally and cause the audience to hang off your next words, wondering what you are about to say. Don't be intimidated by silent moments.
Practice a lot beforehand. If it's for a presentation or a speech, the more you practice it, the more it will take on a life of its own and feel more comfortable to deliver.
Concentrate on one person. Maybe practise in front of them, so that it feels like you're just talking to them.
Connect with your audience. Use feelings and gestures to intensify a point. Just don't overdo the gestures or emotion - a little goes a long way.
Don't look directly into people's eyes. Focus on their foreheads or on a place at the back of the audience, just above the heads in the audience. That way you won't feel distracted.
Let go of assumptions. Just because an audience is not smiling or nodding in agreement does not mean they aren't listening or feeling positive about your talk. People often do not display encouragement on their faces in an audience situation, so don't seek it. You'll know from the applause level at the end how well you went and by then, the speech is over!

[edit] Tips

Practice, Practice Practice! Every chance you get - whether the group is large or small - seize the opportunity to talk to or in front of an audience!
Make certain to speak up with volume (not scream) and project.
Watch your pace and pause if you feel you are rushing; a few seconds breaking to take stock is not noticed by anyone except you.
Make sure you pause in between sentences for greatest effect and to ensure that the talk is sinking into the listener's minds.
Enunciate; clear speech helps those listening as they don't have to decipher the words but can concentrate on the content.
Use vocal variation; it can be tedious and boring to listen to a speaker whose voice sounds monotone and flat the entire speech.
Hold your hands in front of you at waist level. This enables you to make subtle hand gestures to illustrate your point while not causing too much distraction to the audience.
Introduce your topics as questions which you then answer to keep the audience interested.
The uses of "uh", "um", "and yeah", and other similar phrases branch out from the need to fill the silence. Learn to use silences to your advantage, and not to be terrified of them. Pausing to take a breath, recollect your thoughts, and make a greater impact on your audience is perfectly acceptable and encouraged. It is difficult to remember NOT to say "uhhhh ..." but if you try to adopt a mindset that is not against a moment of silence, it will be easier. Practicing will make it second nature, and you will never feel the need to say "um" again.
Listen and watch great public speakers and try to analyze what is it that makes them successful.
Don't be embarrassed by your faults. Demosthenes was a prominent orator in ancient Athens even though he suffered from speech impediments. A good public speaker can overcome these difficulties.