Two things that I have found come in handy from one of my other hobbies of modifying watches is a dust blower and watchmaker's putty such as Rodico.
The dust blower is good for removing loose debris from reflectors, lenses, etc. without introducing moisture from blowing using one's breath.
Rodico is great for removing more persistent debris and oil such as from fingerprints as well as for picking up small parts without damaging delicate finishes. You knead the putty and shape it to however you require and dab at the target.