Mechanical watches are more robust than people expect and fail in predictable ways. Most of that is avoidable.
The crown
The single most common cause of water damage is a crown left unscrewed. Screw it fully down after setting the time, every time.
Water
A rating of 30m means splashes, not swimming. 100m is fine for swimming. 300m is for diving. Ratings assume the gaskets are fresh, which they are not after a few years.
Servicing
Every five to seven years for an automatic. The oils inside dry out, and running a dry movement is what turns a service into a repair.
Day to day
Keep it away from magnets — laptop speakers and magnetic phone mounts are the usual culprits. Wipe the case with a soft cloth. Do not set the date between 9pm and 3am, when the date mechanism is already engaged.