Imagining your Gem like an alive creature you will simultaneously understand that your gem has certain needs. Needs that if you neglect, your gem's "vital energy" will be reduced and in a way it might get even sick! You have to understand that each time you use a crystal or gem in a ritual your gem consumes energy (if your spell is projective like a love spell) or stores - imprisons energy (if your spell is passive like a protective shield). Your gem now needs care. Even if you wear (let's say) an amethyst to be protected by evil eye and negative influences, your precious gem should be handled with care once every new moon! In this way your gem will be full of energy and do its best for you!
1st step. Take your crystal or gem and leave it few seconds under cold running tap water or spring water! Cold is preferred because it corresponds with Earth. This will remove the minor negativities, energize the system of the crystal and start its energy replenishing.
2nd step. Now fill a bowl with tap water (or spring water) and add thick salt in it. You can add Holy Water if available! Now leave the crystal in it (the water should at least cover the whole crystal) for at least a day! The Salted Water equals Holy Water. This will break all energy connections that have possibly been established with negative or even evil entities. Gems which are used in protective spells might also been injured by ghosts, vampires and even demons!
3rd step. Now that you have banished anything negative from your crystal you need to start the healing process. Burn some Sage and let the smoke cover your crystal for few seconds! Sage has unique healing properties in Humans, Animals, other Plants and herbs and even crystals! After you've done cleansing it with the purifying smoke of Sage you can add few drops of the essential oil of Lavender on it. Lavender has also healing and balancing properties. It will restore the euphoria of your crystal.
4th step. Now the only thing left to do is to energise it with the power of the Sun (if your crystal corresponds to Masuline energy like the Ruby) or the power of the Moon and the Stars (most likely; for example if you are curing a Moonstone). If you figured that Sun is what your crystal needs leave it from Sunrise till Sunset so that Sun will send his precious life-giving energies to your crystal. However if your crystal needs the charms of the Moon and Stars leave it outside from Sunset till Sunrise.