Clean the barrel with airsoft gun cleaning kit from the dust after use your airsoft guns, especially in sand environment.
Only buy recommended brand of pellets for your airsoft guns. Deform pellet cause airsoft guns jam.
Use high polish pellets for your airsoft guns.
Reload your magazine with new pellets. Reuse pallets will make your barrel dirty and cause airsoft guns jam.
Stop firing your airsoft guns. Firing airsoft guns jam could damage your airsoft guns.
To preserve the spring of magazine, remove all pellets from your magazine from your airsoft guns after use your airsoft guns.
Keep your airsoft guns dry.
Lubricate your airsoft guns with 100% silicon oil. Using oil will damage your airsoft guns.
For airsoft gas guns, lubricate after 1,000 - 3,000 shots, 3,000 - 6,000 shots for electric airsoft guns or airsoft spring guns.

Discharge your battery of electric airsoft guns before charging to make sure that battery is able to achieve a full charge.
Discharge your battery of electric airsoft guns before store it for a long time.
Remove the battery from your airsoft guns before store your electric airsoft guns.
Charge your battery of your electric airsoft guns until it full. Unplug the battery of your electric airsoft gun from your charger before the battery of airsoft gun or longer than recommended will damage the battery of electric airsoft gun.
Only use battery in perfect condition. Using overheat battery will damage your electric airsoft guns.
Firing your electric airsoft guns continuously more than 6 seconds will overheat your airsoft guns and it will damage your electric airsoft guns.
Changing the mode selector while firing could damage your electric airsoft guns.
After done firing your electric airsoft guns, change in semi automatic mode and firing a few shots to decompress the gearbox spring.

When expelling gas from your airsoft gas guns, do not use the release valve because it can freeze the O ring and cause gas leakage.
Leave gas in the magazine for one or two shots. To make sure your airsoft gas guns in this condition, empty the gas from your magazine then fill burst for a second. Leave the magazine of your airsoft gas guns in full gas or completely empty will damage the seal in the magazine.
Related Link :
How to Clean Airsoft Guns
How to Fix Airsoft Guns Jam