Carmine Gallo, presentation coach and author of the upcoming book The Presentation Secrets of Steve Jobs (McGraw-Hill, October 2009), has counseled many executives on how to give a great presentation. He's also witnessed many common—yet avoidable—presentation errors that people always seem to commit.

Here are Gallo's top five ways that people ruin their presentations and his strategies on how to avoid making them. Above all, Gallo says, remember that the most engaging speakers have a simple secret weapon: "They practice much more than the average presenter."

1. Talk Too Long

"Nobody is as interested in you as you think they are," Gallo says. Most people listening to presentations tend to tune out after about 10 minutes, Gallo says, based on expert opinion and research in cognitive functions. So keep the presentation to less than 20 minutes.

"Look at some of the great speeches over our history, John F. Kennedy's or Barack Obama's speeches, and they're able to galvanize the nation in speeches that last under 20 minutes," Gallo says. "So do you really need to two hours to get your point across?"

Gallo's Tip: If your presentation has to be long, break it into 10-minute chunks. "At every 10 minutes or so, try to reengage the audience with something different—don't just keep showing slides," he says. Try inserting a short video clip, introduce a quick demonstration, or have another speaker get up and briefly present. "Try to find some way to break up the presentation into manageable chunks of time," he says, "so people don't get too bored."

CIO.com: In the "so bad it's good" category, we honor 8 PowerPoint slides (including Bill's) that will make you say, "What were they thinking?"

See: 8 PowerPoint Train Wrecks

2. Kill Your Audience with Bullets

"People who are experts in design say that bullet points are the worst way to learn and impart information," Gallo says. "Yet what is the standard template in PowerPoint? Title and bullets. The standard template makes it easy to be boring."

The term "death by PowerPoint" rings true with most people for a reason.

Too many presenters stick to the PowerPoint template, Gallo says, then cram as much information into bullets as humanly possible—making it exceedingly hard for people to read the slides. And then the audience gets bored. And people start checking their BlackBerrys. (To see eight of the worst PowerPoint slides ever created, see "8 PowerPoint Train Wrecks.")

Gallo's Tip: First off, don't bash the software; bash the person using the software, he says. Second: Don't make every slide look the same (i.e., Title, Bullets; Title, Bullets). Gallo suggests that you use images with little or no text on slides to discuss ideas or concepts, which is also a great way to engage the audience. This will also, he says, "give the audience's eyes a rest every so often."

3. Fail to Rehearse
"I can't tell you how many times I work with executives who spend thousands of dollars on the actual presentation—in creating the presentation and on meetings to create it—and then they don't even rehearse it," Gallo says. "When you prepare and rehearse the presentation—out loud, over many hours and many days—you'll come across as much more engaging as a speaker and effortless."

Gallo says he's learned (from his research and talking to people at Cisco) that CEO John Chambers, who is known for being a terrific public speaker, rehearses quite a bit. "He will go over the slides and content of slides during many, many days prior to conference," he says. "He has internalized the content, and he's very fluid and smooth. And that's because he rehearses."