Three common mistakes I’ve seen #FOSS people and other #introverted geeks make in #PublicSpeaking…well, as an introverted #FreeSoftware geek myself, these also things I have to keep in mind when I speak.
Slow…down. Speak at a consistent, slow speed. This ensures people don’t miss things, you get time to think, and people get time to absorb the information.
Speak loudly. There’s a limit to how much the microphone will do for you. Sometimes you won’t even have a microphone (e.g. when hosting outdoor #OpenStreetMap mapping parties) - learn to make yourself heard without one.
Don’t trail off. End your sentences with a consistent volume and pitch.
So how slow, and how loud? In a lot of cases I’d say WAY slower than what you call slow, and WAY louder than what you call loud 
There’s more, but this is the foundation of any talk. The best content in the world means nothing if it doesn’t actually reach your audience.
A lot of this is useful in everyday life too. Start practicing! 