Not updating the software and firmware when prompted by the phone itself
It’s the hardware that serves as the “body” of your phone, and the software that serves as its brain and soul. Downloading software from unreliable sources can make the phone malfunction, shut down, or can result in all of your personal information to be transferred to an unknown person.
Not cleaning the inside of your phone
Do not avoid cleaning your phone on the inside — tons of dust and small pieces of garbage and dirt from your pockets and bags can make their way into your phone and interrupt the inner workings of the device (like make it slow, for example). If you’re bad at dealing with technology, ask a professional for help.