For a good write up on some common programming mistakes and how to properly avoid or mitigate them, check out this excellent article by Paul Tero. Not only you get an explanation of the mistake, but he also gives you some tools and techniques to use alongside. What i really appreciated as well about the article is that Paul is not shy about admitting to past mistakes, no matter how serious, which helps give perspective about their repercussions and is without a doubt a sign of experience and maturity. Insightful to say the least, I have made some of these mistakes and picked up a few best practices from him:

My Favorite Programming Mistakes.