I tend to swing my hands around a little and fidget. This is because I'm pretty nervous when I present.
I have to be aware of what my body is doing be in control at all times.
Sometimes, I get confused on whether I said something correctly and I stop midway to think.
Or someone asks me a question that I can't answer fluently. This disrupts the flow of the presentation and tends to lead to the audience losing their attention.
Make sure that I am familiar with the content of the presentation like "the back of my hand".
I tend to slur my words together or mutter.
Pronounce each word with carefully and deliberately, especially the "d", "b", "s".