Always lock your device, don’t leave it lying around open. That way a password will need to be entered to activate the device.
A strong password includes a combination of upper and lower case letters and numbers. Never store passwords on your phone or tablet and keep your password a secret!
Keep the software on your phone up to date. Most manufacturers offer updates regularly which often include security updates.
Try not to use unsecured Wi-Fi networks in public areas to access your email, purchase things or do your banking online. If a network is easy to access by you, then it will be easy to access by potential hackers.
Take care when downloading apps – if something looks too good to be true, it probably is! Likewise, don't click on links unless from a trusted source, and be particularly careful if you unexpectedly receive a link to a banking website. (from bbc.co.uk)