To prevent others from physically accessing your phone and all of its data, set a PIN number to lock your phone. This number would have to be entered for anyone to unlock the phone and use it. Pick a number that isn’t obvious (1234 is not a good one!) and memorize it.
There are other means through which your phone can be accessed remotely – Bluetooth connections, SMS (text messages), spyware, malware and/or other viruses. Another risk is connecting through public Wi-Fi hotspots; others might be able to see your information, or you might connect with an “evil twin” hacker hotspot that will try to steal your login credentials. Be cautious with your device: do not accept unfamiliar Bluetooth connections, and do not download any software from SMS or from any unknown/untrusted sources. To learn how to avoid mobile viruses, read the tip “How do I protect my mobile phone against viruses?”