Blunders to Avoid
There are some things that can slip into a presentation that will destroy all the good work you've put into it. Typically these involve spelling and grammatical errors.
Your audience will typically consist of people from many different backgrounds with different types of education. You want to convince them that you are well educated and intelligent. That way they can believe what you say. Giving them the impression, through blunders, that you are not competent will ruin your efforts to persuade them.
Spelling errors are the most likely thing to make you appear to be uneducated, and will cause the audience to quickly form a negative impression of you. You might be the smartest technical person in the world, but if you have spelling errors in your presentation the audience will probably think that you're not that smart after all.
The good news is that PowerPoint will help you in this area. PowerPoint has a huge dictionary, and if it sees a word that it doesn't recognize it will underline it in red when you're entering text. However, this red underline will not appear when you're giving the presentation. Although PowerPoint has a large dictionary it is an all-purpose dictionary, so many technical terms will not be in it. Therefore, a red underline does not always mean that something is wrong – just that PowerPoint can't recognize it. Any time you see a red underline, you should examine it carefully to make sure it's what you meant to say.
PowerPoint has some intelligence in understanding what you wrote. When it sees something that is spelled correctly, but may not be good grammar, it will underline the text in green. Since presentations usually use phrases, this grammar check is usually pretty coarse, but it is still helpful. For example, you might have an item where you've mixed a plural subject with a singular verb (e.g., "We was surprised"). Each word in the phrase is spelled correctly, but the phrase has improper grammar. PowerPoint will underline the phrase in green so that you'll see the mistake. As before, sometimes PowerPoint will mark something in green that is, in fact, what you want.
In any case, you should always look at things that are underlined in green to insure that you really meant what is said.
Sometimes you can make a mistake that PowerPoint will not be able to see, but will still hurt your image. For example, consider the shaft in a car that connects two wheels together. This is called an axle (note the spelling). In ice skating, the only jump where the skater takes off in a forward direction is called an axel (note the spelling), named after the person who did the jump successfully the first time. Both words are pronounced the same way, are valid words, and look almost identical, but mean totally different things. PowerPoint accepts either word. If you're presenting material about a vehicle, it would be very easy to use the wrong word, and PowerPoint will not tell you there's a problem.
Your only defense here is to review your presentation carefully, and not just trust PowerPoint to catch any errors. You should also have the entire team review the entire presentation looking for errors. Usually an error like this that would escape the notice by one person will be caught by somebody else on the team, saving your embarrassment.