The fundamental NRA rules for safe gun handling are:
A gun brought out of prolonged storage should also be cleaned before shooting. Accumulated moisture and dirt, or solidified grease and oil, can prevent the gun from operating properly.
Before cleaning your gun, make absolutely sure that it is unloaded. The gun's action should be open during the cleaning process. Also, be sure that no ammunition is present in the cleaning area.
This information was taken from the NRA web site: http://www.nrahq.org/