On your Altar, you may like to have representations of the elements, Goddess statues/pictures, a pentacle (if you're Wiccan) your goddess journal and anything else you like! Dont put on anything that isnt sacred though, this is a holy place for you and goddess only!
If you are working with a particular goddess, you may like to put things on your Altar that are sacred to her.
Check out 'A book of Womens Altars' for further inspiration!