A mechanical watch is built to run. Regular wear and a few calm habits are more useful than constant worry.
Wind and set it deliberately
If the watch has stopped, a few turns of the crown give the movement a reliable start before wrist motion takes over. Set the time with the crown pulled to the correct position and avoid forcing any function that feels blocked.
For a date movement, avoid quick-setting the date while the mechanism may already be changing it. If you are unsure, move the hands away from the late-evening and early-morning window first.
Keep it clean and away from magnets
Wipe the case and strap after wear, especially after sweat or salt. Strong magnets in speakers, tablet covers and tools can disturb mechanical timekeeping. If the watch suddenly gains or loses far more time than usual, magnetism is one possible cause.
A watch is not harmed by sitting still for a while. If you rotate several watches, let them stop and set them again when you return.
Service when behaviour changes
There is no single service interval that fits every owner and movement. Pay attention to declining power reserve, difficult winding, condensation, impact damage or a clear change in accuracy. Contact the maker when the behaviour changes rather than waiting for a small problem to become a large one.