The Number One Proofreading Rule
Browse the web for ten minutes and you'll find the usual suspects of proofreading tips.
Proofread for only one error at a time.
Read slowly, and read every word.
Read the document out loud.
Separate the text into individual sentences.
Walk away from the document for a day or two.
Read the document backwards.
A few years ago I attended the Bar Association of the Fifth Federal Circuit's appellate conference. The conference hosted a panel of Fifth Circuit judges who lent us their thoughts on writing and writing style. When they opened the floor for questions, one of the lawyers sitting in front of me asked the judges for their best writing tips. Judge Jennifer Elrod spoke up. She said: Use a ruler. "There is just no substitute for sitting down and going through your document line-by-line with a ruler." She said she does it with every opinion she writes. Honestly, I didn't immediately jump on this tidbit; I guess I thought I was just too smart to play with a ruler.
Some months later, I ran across this typo long after the brief had been filed (sometimes auto-correct is not a great help). I decided then that I wasn't all that smart and I bought a ruler. I've been using one ever since. I can't say how many mistakes—it's probably well into the thousands by now—I've corrected all because of that ruler.
Judge Elrod's rule on the ruler should be every writer's number one proofreading rule.