Go to church. There is no better place to be for inspiration and understanding the special themes and terminology of gospel music. The word "gospel" literally means "good news," particularly the good news about Jesus' life, ministry, death and resurrection. It is impossible to write meaningful gospel music without first understanding these concepts.
Pay attention to the sermon. The vast majority of the content of gospel music is found in the sermons preached on Sunday. Pay special attention to themes about overcoming adversity and celebrating Jesus' birth and life as these feature frequently in the genre.
Listen to the greats. Gospel singers like Aretha Franklin, Marion Williams and Blind Willie Johnson are a wealth of information for the aspiring songwriter. Listen to how the lyrics and the music interact, as well as how the performers' particular talents enhance the presentation of a given song.
Get out your pen and paper and start writing. Write music every day regardless of your mood. Turn to the Bible for inspiration and themes to choose from. If you cannot read music then start taking piano lessons. In the meantime you can record yourself singing your songs so you can remember them later.
Take your music to the choir director at your church. Have him look over what you've written and give you pointers on how to improve. Once you have made sufficient progress you should ask to have some of your music performed on a Sunday. Once you gain experience in this arena, start recording the Sunday sessions and sending them to record companies. Your new career may well be under way.