A child's pacifier should be washed or sterilized daily with soap and water to keep any bacteria off of it.
If the baby has dropped their pacifier on the floor wash the pacifier with soap and water before giving it back to them.
When my kids used pacifiers I would keep extra clean pacifiers available so that I could immediately give the child a new clean pacifier while I washed and cleaned and sterilized the others ones.
I would first wash the pacifiers in hot water and dish soap and then get some water boiling and dip the pacifier into some boiling hot water to help kill off any germs.
The hot water and dish soap is usually enough but dipping the pacifiers in some boiling water kills off more germs that may be on the pacifier and also ensures that the soap is removed fully from the pacifier.