Digital photography tutorials are fond of introducing the Rule of Thirds to neophytes as a useful compositional aid. Indeed it is. But a far more useful rule that I rarely find mentioned is the Rule of Threes.
This is another very basic rule, and is one I found to be more essential than any other. Simply, whenever I capture a digital image that I want to keep, I make sure that it is copied twice onto a separate hard drive, or DVD or flash drive. I always keep at least three copies of all my photographs. Overkill? Well, once no less than two of my three copies have become lost through drive failure. Only having the third saved me. In many case, I have gone further with four or five separate copies. It's the smartest thing I do.