If you have boxes or bins in your basement or attic, you should label the contents so that its easy to find things later on. This is pretty obvious, but most people don't do it and they pay the price when it comes time to look for things.
Use White Duct Tape
I highly recommend using White Duct tape to label the storage containers. This makes it easy to identify what's in the storage containers as the tape is strong enough not to fall off in the heat and cold. The tape can be easily removed or replaces as contents of the storage container changes. I tried using labels and they fall off pretty easily.
You should tape one side and the top of the box so that its easy to identify stacked storage containers. Also be sure to label exactly what's in the box, saying "Christmas Decorations" isn't too vague. A better solution would be, "Snowmen and Raindeer for fireplace." The more descriptive you are to what's in the container the better off you will be to finding what your looking for.
Boxes of Books
If you have a box full of books, take the time and record the title of the books and tape it to the box. The few minutes that you spend on doing this will save you a lot more time later! Also you may find that some of the books aren't worth keeping anymore.