For a mechanical watch, expect to overhaul the watch every 5 to 7 years. This type of work requires the watch to be taken apart, components cleaned and lubricated, reassembled, gaskets installed and timing adjusted.
A fine watch is meant to be worn and enjoyed. It is a lubricated machine that is engineered to run 24/7. The key is to keep a good watch wound and running. There are sophisticated oils used for maintaining watches. For example, Rolex® watchmakers use four different oils for different parts of the watch movements.
One can either wind a mechanical watch (whether manual or automatic) to keep it running or use a watch winder to keep automatic watches wound.
Expect to have a quartz (battery) operated watch overhauled every 7 to 10 years. They require less service work but will require a watch cell replacement every one to two years. Water resistant types need gasket replacements when cells are changed.