What advice can you give Christian writers?
First of all, I think the whole label "Christian writer" is a problem. It is fine to write to the cenacle of other Christians every now and then, but don't consent to be ghettoized by the secular world. Every baptized member of the Church has something crucial to say to the world outside our church doors. Be an apostle to the 21st Century and start by thinking of yourself as a writer who is a Christian.
Secondly, find out what your talents are and then develop them to the maximum of your capabilities. Don't look for an easy life, but set your face in the wind and commit yourself to being what you have said you are, a writer. Stand on the shoulders of the great writers who have come before you and be teachable.
Know that, commerciality for you as a writer will be in the cross-section of the passion of your heart with one of the agonized "Whys?" of the people of your time. Everything else you write is preparation or therapy.