1. Read a script
It's a common misconception that people giving a presentation have some notes or bullet points to generally remind them of what to talk about. In reality, even the best presenters are reading word for word a pre-written script. Those that appear not to have a script, have memorised one - just like actors do.
Example of presenters reciting a memorised script
When an MP stands up in the House of Commons and gives a speech, it appears like the ones who are not referring to notes are making it up as they go along. In actual fact, they are all reciting, word for word, a script that they have memorised. This always has to be the case because MP's are required to submit their speech, in its entirety, word for word, in writing before they present it.
Ted talks
When you watch a Ted talk, the accomplished presenter is often walking around a stage, talking freely, without any notes and they do with great confidence and style. They are amongst the top presenters in their professional field. However, they are actually reciting a script that they have memorised. Ted talk preparations insist that they memorise a script and practice, practice and practice until the words are so embedded in their subconscious that they cannot possibly forget them. They also have the help of a coach.
A happy medium for mere mortals
Memorising a complete script takes a lot of time. Also, reciting a memorised script in private is very different to standing up in front of a conference audience and reciting it. That requires great confidence that only comes with experience. A happy medium is to memorise as much as you can but still follow a script in front of you so that you can keep referring to it. The fact that you have memorised it will greatly help it to flow and sound natural. If a script is presented many times, large sections of it will naturally become embedded in your memory.
2. Think about rhythm rather than word choice
An audience pays very close attention to your presentation style, cadence and flow. Learn how to speak in a comfortable rhythm and only break it when you need to emphasize a point. Training to a specific rhythm keeps the tone of your talk consistent.
3. Practice with a countdown timer
Get used to presenting against a countdown timer. If you do that, you'll be less likely to get nervous as you see the time disappearing.
4. Record yourself
Listen to your self presenting. Focus on your tone and speech dynamics. Critically listening to yourself will help you develop a presentation style.