Everyone who is on a large-scale project can benefit from this simple, yet amazing advice. It's the best way to make sure your code works. It can be summed up as follows:
Work on a portion of your project. Comment thoroughly why each code block exists. Then, check back in a week.
Why? As you are writing your code, everything makes sense to you. Your train of thought is fresh and you don't forsee any errors. However, after about a week or so of not touching your code, the patterns you formed in your brain as you wrote begin to diminish. By the time you return to your code, you are looking with the critical eye of someone who never saw this code before.
Novelists have the same problem: Everything makes sense to them, but nobody else understands it. Then, the author re-reads the passage and says: "Wait. I was trying to say [insert point here]". Then, s/he rewrites it more clearly. This is a good strategy to implement when writing code.
The larger the project, the more you can benefit from this. As I type, I am checking about a thousand lines or so of code. I need my comments; otherwise, it's incomprehensible. Even so, I'm finding tons of things I did that were redundant, prone to error, or just plain wrong altogether.
Of course, those who do programming for a career can't just tell their boss they're taking a week off to "de-familarize yourself" with the project. But that's what teams of programmers are for: To help watch for errors. This advice is better suited for the solo programmer.