Use any method to get steam in a room. Running a hot shower works well, which fills the room with steam. When the steam has subsided, there will be less dust in the air than usual. This is the best time to apply the screen protector.
Wash your hand first and Dry your hands with a clean or disposable towel or air dryer. Use a microfiber cloth to remove most of the grease and dust from the screen. Be sure that the cloth is clean before using it. You want to remove as much dust from the screen as possible, especially if it was just removed from the factory packaging.
Lay the microfiber cloth on the screen to keep the dust off.
Prepare the screen protector. Carefully remove it from its box or packaging.
Remove the cloth from the screen, slowly align the protector, and place it on the screen.
Get a credit card or similar item as a scorer. Use this to carefully remove all the air bubbles.