Having a microwave replaced that is bolted to a wall above a range is not east task. So maintaining your microwave is a must. Be sure to clean any spills or good splatters up right away. The bits of food left behind can absorb some of the microwave's energy when you turn it on again, creating a hot spot that can damage the interior. Take special care not to scratch the protective mesh inside the door if its exposed, because it prevents microwave's from escaping and zapping you.
When using the range cooktops make sure to turn on the exhaust fan. The moisture rising from the pots and pans collects on the electronics and shortens the life span of the microwave. Also you will want to clean the grease filter by simply letting it soak in the sink filled with hot water and degreasing dish detergent. Do not run it empty. Some people mistakenly run their microwave empty when they just meant to use the timer. With nothing in the microwave, there are no water molecules to excite, and the unit can overheat quickly or cause burn marks in the interior.
Another great tip is do not slam the door. All the door strikes, latch mechanisms, and door switches themselves are plastic, so slamming the microwave door can physically break any of these components. The series of switches all have to work in unison. Also very important do not attempt to repair the electronics yourself. A microwave can hold an electrical charge at thousands of volts in its capacitors for hours or even days after it has been unplugged. Lastly avoid putting metal utensils or dishes in the microwave as it can cause actual sparks to start flying.