Most people ware their watch on their non- dominant hand. If they were right handed like most are they wear it on their left hand. because people are most active with their dominant hand by this situation people can't work with wrist watch dominant hand. otherwise there aren't any other rules to wear on left hand. but historically women only use to wristwatches men used pocket watches and the pocket watches became popular during the war period of early 20th century. However there are some interesting stories that we can read in web sites.

Which hand that you use to ware your wrist watch?