I heard once that to sing "properly" you shouldn't make all the "singing faces". Now, I'm not saying I don't do singing faces. I go all John Mayer when I open my mouth, I'm what you could call a cinematic experience, probably in the horror-genre
Anyway, what I'm getting at is when I sang for my mother she used to comment how I would emulate(???) voices and not use of my own. But I think there's a lot of learning involved in the emulation as well. Falsettos, vibrato, high pitch, low pitch, heck... even accents.
I think you need to find your "comfort zone"-vocally, the range you like to sing within and start from there. Develop it as you continue. If you write your own songs, you will probably be one who knows it best and know how to express it. Like Chris said, noodle around and experiment. Find out what kind of music you like to sing and what kind of singing goes along with it.
But the fact of the matter is, I'm still operating with 4-5 different voices
John Mayer, Jason Mraz, Jeff Buckley (and might I add, I should have written "Jeff Buckley"), Dave Matthews.... the list just continues to grow, but I feel I pick up a little here and there, so it can't be all bad
Perhaps someone else should answer the question