Talking about the precautions,
-There are really useful apps available for mobile security with antitheft feature eg."Avast Mobile Security" that should

be installed into each devices.
-Avoid storing precious data in your mobile phone which is vulnerable to loss or theft.
-"Google Device Manager" a really good tool for mobile tracking
-Register with https://3gadgets.com/ or that helps track your Mobile's IMEI no.
Visit cop@vsnl.net or contact cop@vsnl.net for additional details.

Once you realize that your Cell phone is not in your pocket you start panicking and your mind stops working and you don't

understand what could be done in such case below are few important things you should do.
-Search at every possible places where there is a chance of you leaving the device.
-Try calling your mobile no. to see if any one picks up the call.
-Try calling your friends to see if by mistake you dropped your cell over there or they might have borrowed it.
-Still if you cannot find it then file an FIR with the nearest police station.
-Call your operator to block the IMEI no.of the phone.A copy of FIR might be required for doing that.