Once every month, or when performing your regular maintenance, check if your bike's chain has the right amount of tension. Refer to your bike's user manual for the correct level of tightness for your bike. High tension could lead to chain faliure, whereas low tension could cause the chain to slap against the swingarm and damage the sprocket.
Watch the video below to learn more about tightening your bike's chain.
(Video Credits: Andrew Mercer @ YouTube.com)
(CAUTION: Performing this maintenance procedure involves risk of personal injury. Ensure that the engine is switched of before proceding, and wear gloves for protection. If you are unsure about being able to perform this procedure by yourself, get it done by a professional mechanic)