1) Diamonds are hard substances, but they can still be chipped. If you're doing rough work, like moving stones in the garden, it's advisable to remove your ring.
2) Store your diamond jewelry in felt or velvet-lined containers. Metal from other jewelry can scratch a diamond.
3) Hand creams, dishwashing liquid and soaps can cause a build-up of grit on your diamond, lessening its brilliance. Gently scrub it away, with a soft tooth-brush and warm water. You could also soak your diamond overnight in a tiny bit of window cleaner. Doing this once a week will keep it sparkling. Rinse it and polish it dry with a soft cloth. Polish gently to avoid damaging the prongs in the setting.
4) Remove your diamond ring when working with strong cleansers and chlorine bleach. These can wear down the settings holding the diamond.
5) Ensure the setting is always secure. If it feels at all loose, take it in to a jeweler for immediate repair.
6) Insure your diamond.
With care, your diamond will last a lifetime and always retain that luxurious brilliance.