BBs
The first thing to remember, and perhaps the most important part of proper airsoft gun maintenance, is to use quality BBs. Some BBs, like the BBs most airsoft guns come with, are too light or carry surface imperfections that can damage the gearbox of your airsoft gun. Use BBs that are at least .2g or heavier. Never re-use BBs, as once fired they become chipped, scared or covered with contaminants that can jam your gun. Do not use lead or copper BBs, or any foreign objects.
Use
Remember when using your airsoft gun is that it is not, in fact, a real gun. Most are not made of metal or wood, and will not stand up well to heavy abuse. Even dropping it on a hard surface can cause damage. Do not try to hit anyone or anything with the gun itself, even the butt or stock. Do not use a bayonet or attach anything heavy to the barrel. Be careful when using a shoulder sling---pull it too tightly and you could cause damage.
After Use
Wipe your airsoft gun with a clean cloth after use. Remove any dirt, oil or other contaminants. Use a cotton swab on the inside of the chamber and the barrel.
Lubricate your Airsoft gun every 3,000 to 4,000 shots fired. Place a few drops of silicon-based oil into all moving parts of the gun, including the bold, magazine and chamber. Do not use too much oil, and wipe excess oil off the gun when you are done. Over-oiling can lead to jams and will accumulate dirt and grime inside your gun.
Always store your airsoft guns in a safe place, out of reach of children. Make sure the gun is completely unloaded, including magazine and chamber. Store your gun in a cool, clean place. Do not store a gun that is cocked because this will wear out the spring.