Important notes: Selenite is a very powerful crystal, that can very quickly open the Crown Chakra. If you're not experienced working with crystals, do NOT try using selenite when working the crown chakra. Instead, use a clear quartz crystal or amethyst.
Some people find that selenite can leave them feeling a bit dizzy or spacey. For this reason, it's advisable to keep a grounding crystal with you, or nearby, when working with selenite. Some choices for grounding crystals include obsidian, hematite, red jasper or black onyx. As an alternative to this you could do some conscious grounding after working with selenite, such as visualizing roots reaching from the soles of your feet into the ground, walking outside and feeling your connection to the earth, or eating a light snack.
Because selenite is associated with Higher Truth and our relationship with the spiritual plane, it's not a crystal to be kept stored away in a drawer or used merely as a decoration. Good owners of selenite will respect it, and work with its energy in a cooperative manner every day.