Here is a technique I use every week while proofreading final drafts of this tips newsletter. When you need to proof your final documents or important email, have your computer read the text out loud to you and listen for mistakes. You’ll catch errors you might otherwise miss.
In many OS X applications, you can highlight your text and choose [Application] > Services > Speech > Start Speaking Text (if you are using Mail for example, look under the Mail menu next to your Apple menu).
As with last week’s tip, this trick only works in Cocoa apps. If you are using an Adobe or Microsoft program where this doesn’t work, just paste the text into a new TextEdit document and have your Mac read from there.