Cover each foot of your bed with furniture cups. Furniture cups fit over the feet of most bed frames, and they offer the bed increased friction against the hardwood floor. Choose from very plain or decorative furniture cups, or cups that also act as bed raisers and give the bed several more inches of height.
Lock the wheels on your bed. If you have a bed frame with wheels underneath the feet, the wheels typivally have a lever that locks them into place. Check to make sure that all of the levers are down, as they can become flipped over time.
Insert a wooden or plastic shim underneath each foot. The shims should be inserted from different directions under each foot to further increase the drag. Both plastic and wood shims are widely available from the hardware store, and wood shims can be stained to match your floor.
Place an area rug underneath your bed to prevent it from sliding. An area rug also adds color and texture to the room. To further increase the friction against the hardwood floor, place several sheets of shelf liner between the rug and the floor.