So, as you would for any partner, protect your investment with some regular attention. Use a good padded case and strap. This protects against the elements, knocks, and theft. Always replace the lens caps when you remove a lens. Clean the lenses regularly.
Special lens cleaning fluid can help with stubborn smudges.
With SLRs, consider adding a UV or skylight filter to each lens for extra protection. Clean the camera in the same manner. The autofocus, exposure and viewfinder windows need to be clean for correct operation. It's amazing how sand and dirt get so easily inside the camera. A can of compressed air may help but make sure it's suitable for photographic equipment.