YA fiction, or Young Adult fiction, is a weird category. First, the name. Not for adults, but for children. In fact, since the typical YA protagonist is 16, the category is clearly for kids younger than 16. (Kids tend to think they are more mature than their years. Kids that read usually actual are.) So YA is aimed at kids in the 12-14 year age group.
Also, for most fiction you have to ‘sell’ the book to the actual readers. In YA, there are other people you have to ‘sell’ it to.
For mainstream YA, you have to ‘sell’ the books to public school teachers and school librarians. Your book must have content that they approve of. These days, the YA gatekeepers talk a lot about ‘diversity’ and want gay and ‘transgendered’ characters, but that’s not the most important thing. Number one is that you must promote a positive attitude towards (public) school, learning, reading and the like. No books with lead characters who are suspicious of schools and literacy!
For Christian YA— Evangelical, Catholic or other— your job is to ‘sell’ the book not to the kids, but to parents and grandparents. Many of a Christian YA books’ sales come from parents and grandparents giving gifts. Some of these books will never get read by the actual child who receives it!
For this reason, Christian YA books must not only be Christian-wholesome, they must be perceived as such by parents and grandparents. If the grandparents are old-fashioned about things like minced oaths or about Christian characters dancing, drinking alcohol, or owning a pack of playing cards, those things must be excluded from your book for it to sell well.
But for a YA book to do really well, it must also be thrilling enough to get young readers excited when the book finally gets to them after teacher or parent approval. We can do that, can’t we?