Huh. Looks like I’m back. I’m writing about myth and legend today.
Myths are an integral part of a culture. It doesn’t work to have, say, a fantasy novel, or a book set in the Palaeolithic, where the characters do not worship. One or two characters might deny the existence of any deities, but the culture as a whole should not.
A website I’ve found useful, both in my study of extant myths and my creation of mythology for my books, is Encyclopedia Mythica, found here: http://pantheon.org/
Also, think about your myths as you design them. It doesn’t do to have your patriarchal culture live in a desert, walled in by mountains, and revere a goddess of the sea. Make sure your pantheon makes sense.