The craft knife blade should be kept clean at all times.
After each use, wipe the blade with a dry cloth to remove any debris that may have built up.
It is important that the blade is not placed in or near any substances, such as liquids, that could cause the metal to rust.
Once a craft knife blade has become dull it is easier to replace it than to sharpen it. An old blade is simply detached from the handle, and a new blade can be inserted into place. For more information, see How to replace the blade on a craft knife.
Storage
When the craft knife is not in use, store it in a safe and dry place, preferably with the blade covered. A craft knife case is probably the best solution.