Your watch should regularly be checked by a watchmaker regarding its functions. Please make sure that the water resistance remains the same (see above). You should try to avoid strong impact and not to drop your watch. Keep it away from harmful chemical substances (especially thinning agents). Furthermore, strong magnetic fields can damage your watch.
For your leather strap it is advisable to use special high-quality care products for leather. Check whether your preferred care product is also suitable for the inside of the leather strap. In, general you should try to avoid any contact with water, especially with salt water. Metal straps should only be shortened by specialists (watchmakers).