In the course of my work, I sit through a lot of presentations. There are some great ones (Guy Kawasaki, Steve Jobs, Brad Ames, and more). And then there are the ones where I wish I could teleport myself out of the room.

I've written about some good presentation skills/aids in the past (see Related Links, below). On the other side of the coin, here is my "don't do it" list so far.

Don't put too many words on the slide. If you want me to read an article, send it to me in email. I came to hear you - and hear your stories from your heart.
No animations, videos, etc. unless they are a crucial part of your story. If you are showing a video clip that helps tell your story, I can dig it. If it's a race car sound effect with a word skidding onto the screen, I don't need that. PowerPoint gimmicks are like the "Reply All" button in your email client - just because it's there doesn't mean you have to use it.
No jokes about getting the time slot after lunch, and how everyone is going to nod off. That's just not funny because everyone says it. Just tell me a story about something, or a good clean joke.
No reading the slides verbatim. Again, I'm here to hear you and your stories. You can use the main points to jog your memory, but tell me something I don't see on the slide (this is even worse when you combine it with #1 and you read a bunch of words to me).
Face me, not the screen. When you face me, I feel a connection and your voice projects toward me. When you face away, I lose the connection. More so if I can't hear you.
Don't use a font that's too small to read from the back of the room. I get the cheap seats sometimes but I still want to see your slides from way back there.
Don't use a text and background color combination with low contrast. Dark blue on black (yes, I saw that recently) doesn't cut it from anywhere in the room.
Avoid busy / heavy background graphics. Text gets lost on a busy background.
Don't talk too fast, and don't mumble. I think this one speaksforitselforatleastitshould.
Don't "wing it." Know your topic, know your slides, and know your key points. It's important enough for me to be here, so don't treat it like improv. Rehearse before you show up.

Not comfortable presenting?

Some ways to improve include:

Find someone who'll watch you and help you develop a "stop / start / continue" list to improve your skills.
Read Beyond Bullet Points and Leading Out Loud to become a better story teller.
Practice. It may not make you perfect, but you'll be closer to perfect with each try.
Videotape yourself doing a presentation and watch it so you can see how others see you during presentations. It's painful at the beginning, but it will help.
Seek professional help. One place I've gotten some excellent coaching is from my friend Jim Endicott's company, Distinction Communication. I swear by their pocket-sized book, The Presentation Survival Skills Guide. Check out their library of articles on presenting, as well.