Proofreading takes more time than most people would imagine. It has very little to do with your reading speed, because the kind of looking, the kind of attention, that it requires is quite different from reading.
Fast readers are usually highly experienced readers, whose eyes take in patterns of words rather than details. Their minds fill in what should logically be there, given a certain pattern, rather than what actually is there on the page, or on the screen. For proofreading, they will need to slow way down and use deliberate techniques to observe what actually is in the work they're proofreading.
Do not expect to be able to proofread more than 8-10 pages an hour, which is about 2000-2500 words an hour. If the text is highly technical, densely written, or has a lot of special formattings, such as with graphs or tables, it will go more slowly than that.
Slow is good! Do not aim to be fast. Aim to be careful and accurate.
So the first principle of proofreading is to make sure enough time is allotted for it prior to any deadlines.
Let's first look at situations where you are proofreading your own work – something you have written. Do not try to proofread your work right after you've finished writing it. Why not? Because what you meant to say, what you intended to write, is so fresh in your mind that you will have a tough time seeing what you actually did write.
It's best to let your blog post, chapter, or whatever sit at least overnight. If that's not practical, at least get up from your desk and do something for 10-15 minutes that takes your mind away from your writing, such as making a phone call, reading the newspaper, doing some pushups with the TV on, and so on. A fresh mind is needed to catch mistakes.
You also need alertness. If you are mentally and/or physically tired, it's not the right time to proofread.
If you're proofreading something someone else has written, make sure there will be enough time after finishing the proofreading to check with the author if there's a question about something in the text. For example, suppose someone wrote that an event was going to take place on Thursday, September 23, but this year September 23 actually falls on Tuesday. Which is correct there, the day of the week or the date? Did they really mean Tuesday, September 23, or Thursday, September 25? This isn't something you can settle by looking up a reference work, and a lot may be riding on it.
Now when in the production process should proofreading take place? Let's say you have something that's going to be printed on paper. You need to proofread when you have the text laid out in the format that is going to the printer. If you proofread before it's laid out, you'll miss changes and mistakes that take place during the formatting process, like lines dropped here and there, headings put in the wrong font, headlines corrupted when shortened to fit the available space, and so on. Likewise, for something that's going to be posted online, proofreading should be the very last step of the process, after the text has been laid out and before the "publish" button is hit.
Next, we get into the meat of the course, the five best proofreading methods.