Care of Deities
Deities that you have on your altar may be statues, pictures, or items that symbolise a deity, like a shell for Aphrodite.
But no matter what it's made out of, an altar deity is not just a thing.
It is the Divine.
Anything that is venerated as a goddess or god becomes Divine. You may not be able to sense it, at first, but it happens.
So treating altar deities with respectful care is very important. As you treat Her representatives, so you treat the Divine.
Cleaning Altar Deities
The great way to tend to altar deities - besides making offerings - is to get a couple of new makeup brushes. A fat fluffy one, and a narrow one will take care of any dust that accumulates.
Keep them specifically for tending your altar.
When you are going to handle a deity, it is respectful to bow or lambaste or in some way greet Her, and share your intentions.
Then handle Her gently and with care, as you would a baby in your care. And when She is refreshed, set Her back with another bow, and gratitude for Her presence.
Keep the Goddess fresh and well-loved on your altar, and She will be strong and happy in your life.