Never send private information like bank account details, PINs or passwords through WhatsApp.
Never accept files or begin downloads from messages sent to you by strangers or unknown numbers.
Never respond to suspicious messages that come through from unknown numbers.
WhatsApp as a service will never contact you through a WhatsApp message. Never trust any message that claims to come from WhatsApp and demands some payment for the service.
Some scams say they can connect your PC with WhatsApp and send messages from a desktop. Do not believe these as this is not possible.
Keep automatic downloads disabled so that you can always keep a check on what is being downloaded.
Avoid using WhatsApp when you are connected to open Wi-Fi networks. These are hunting grounds for malware authors and data sniffers.
Always keep an updated antivirus security solution installed and updated on your mobile device.