What I try to do when creating maps is look at things I like, like Preach said. I usually look at other MMOs I'm fond of though, & get my inspiration from them. Not neccessarily copy, but if there's a certain 'style' you like, go for it! <3
I can give a few but first, think of some maps you really wanna do. It can be a apocalyptic map, a warrior cat map, or something mythical. Maybe you do a map based on harry potter or some type of movie you've enjoyed previously. That's where inspiration really comes from. Either book or movie.