How can I create a safe sleep environment for my child?

No stuff in the crib. This is presumably referring to a baby. There is no question that if the issue is safety, the most important thing is to decrease the chances of injuries and sids. So this means for infants, no blankets or pillows or bumpers or wedges; for toddlers still in a crib, no bumpers or other objects than might enable strangulation or a toehold for climbing out (or even better, move out of the crib!).
CPSC.GOV. Your baby should always sleep in a crib or bassinet that meets the latest safety guidelines. If you receive a "hand me down" product you should check the cpsc.Gov website for safety information and product recalls. In addition always put your infant to sleep on her back.