1. Use the native device security to setup a pass-code/pin. Do not use swipe patterns as they may be easily detected by the smug marks on your screen. Use at least 4 numbers in your pin but you should use at least 6. It takes 18 minutes for someone to hack in to a phone with only 4 numbers. It takes 18 hours to hack in to a phone with 6 numbers in the pin.
2. Use a trusted mobile device security application.
One of the best applications I have found is Lookout (https://www.lookout.com/). This app works with android, iPhone, Kindle Fire. What I like about this app is that it does it all! If you have a pass-code/pin setup, and someone tries to hack into it, after 5 attempts, it will take a picture of the hacker from your front camera (if you have a front camera) and will automatically email you the picture. It will also allow you to locate your device using Google maps.
3. Avoid questionable applications. Only download applications from Apple's iStore, Androids Play Store, or Amazon's App store. Apple's iStore is very restricted as to what applications can be placed on their store. Android and Kindle apps are less restrictive but some evaluation is done prior to allowing applications to be placed on their stores. DO NOT open your device to allow installation of apps from sources other than the devices native application store.
4. Be aware of your surroundings. When in a public WiFi area, avoid having your Bluetooth device active. Only use public WiFi areas that require you to confirm or login to the WiFi with a specific password/code. Do not leave your mobile device unattended or someplace the device can be easily stolen while you are not paying attention or distracted.
5. Keep your mobile devices' operating system (OS) and security applications up to date as much as possible. The manufacturer of your device will provide updates from time-to-time that may contain security updates native to the device and operating system. Your security application (such as Lookout) will provide updates for the application itself to recognize the latest virus and malware threats.