Something tells me that you're using a forehand grip and therefore serving with an open face. You should be using a continental grip. Also keep the racquet face closed until contact, which means throw the racquet upwards toward the ball with the racquet sideways, you're forearm will naturally pronate right before contact. I personally use an eastern backhand grip on serve, but I usually advise those who are trying to learn a basic serve to use the continental. But you can play around with an eastern backhand to see if it's more comfortable for you.
But like like Dmast said, at the very least, a description would be helpful. This way we know you are doing everything else correctly.