I suppose if you wanted to split hairs, you could technically consider the LDS faith to be polytheistic, since Mormons believe God the Father, God the Son, and God the Holy Ghost to be separate and distinct individuals.
Outside of that, it's pretty simple. Mormons worship God the Father, through the Son. While we believe that there are other gods out there, they are not our God. I find that an analogy helps me think about this clearly: At work, I have one boss. He is my boss and no one else is. There are other bosses, but I do not report to them, they do not affect my quarterly reviews, and I don't really interact with them in any sort of manager-underling relationship. The same goes for God.