Know your stuff before going on stage. Whatever you are speaking in public, learn the topic by heart and you should do just fine.
People remember stories better. If you are giving a pitch or a talk, consider telling a story related to the topic you want to talk about.
Rehearse. Record audio and video while you are talking. You can more easily spot the problems.
Most people say hmmm filler words like like hmmm these in their sentences.
Slow down. Talk slowly, breath slowly and have pauses here and there. Gives you more time to think ahead and you seem more confident. Also allows people to think about what you have just said. Say the most important parts even slower.
Keep your audience engaged with your voice. Avoid speaking in monotone. Change your timing with pauses and change the volume of your voice. You can outright yell parts of your sentences with no apparent reason.
Compilers are jerks, right? RIGHT? OH YES THEY ARE!
Keep your audience engaged with your movement. Use minor hand movements when speaking. Slowly walk around the stage if possible, but always face the audience when talking.
And as we came from lunch... *place your hands front, left side and start sliding them to the middle* ... he was wearing this the most ridiculous hat. *move your hands over your head and bring them down, like placing a hat*
Keep your audience engaged with your content. People will remember you a lot better if you get them to laugh in first 30 seconds to the talk. Surprising your audience every 30 seconds is a good way to keep them engaged. Pretty girls also work, but include only one per presentation.
[Show picture of a mansion.] I bought this house last week. *GASP* Nah, just kidding.
Focus on up to three main ideas. No one is going to remember half of you say anyway.
Avoid explaining. Avoid using terms that listeners do not understand. Prefer being too simple than too complex.