Protecting your smartphone from hackers is probably one of the smartest moves you can ever make. There are some key steps you can take to decrease the chance of it happening.
The first relates to your security mindset. Don't assume that it will never happen to you - behave as though it might, and take action. Password protecting your phone is the most obvious, and simplest, thing you can do. However much you trust someone, never share your password, or if you do need to, change it straightaway.
Be careful about the information you store on your phone. Hackers are after sensitive personal data, like bank records. Don't use your phone for banking or personal affairs unless you absolutely have to, and then delete the information as soon as you have backed it up on a PC or tablet. Leaving personal data in your phone for lengths of time leaves you vulnerable - a phone containing nothing more than chat and photos isn't worth hacking.
Next, consider the strength of your password. Too many people use anniversaries or birthdays - don't be one of those people. Choose a unique password for each phone you own, and create it from a combination of upper and lower case letters, as well as numbers. Change it regularly, and if you need to write it down, store the information separately from your phone.
Password protect your voicemail, too. If your smartphone allows you remote voicemail access, you are particularly vulnerable. Contact your phone retailer if you don't know how to do this.
Finally, if you have Bluetooth, disable the 'Discoverable' mode that allows your phone to be detected by scanners, and install any security software which your phone will support. You can't stop hackers, but you can protect yourself against them by making your phone as secure as possible.