Here's what I've found:
- Not every reader is the same faith. Be vague about the church name.
- Don't use any specific way to baptize the person, or do use any other specifics for a given church.
- Do specify if it's a protestant versus Catholic church, for example
- Specify if it's mainstream or fundamental protestant, just to be clear.
- Don't judge others in the story for having a different religion
- Keep the preachiness out. Others might have different ways to worship than at your church.
- When quoting the Bible, keep the number of verses to a minimum (I try to keep it to less than five, if possible). If you need more thoughts from the Bible, paraphrase so no specific Bible is overquoted.
- If you do quote the Bible, make sure you put something at the front of the manuscript that describes where you got the Bible quotes from. If you don't know how to quote your specific Bible, go to a search engine and type in 'how to quote the Bible in a book' to get the information. I also stay with just one Bible for quotation, if possible. I think in one of my books, I used two (King James and New International Version) because a deceased character used the King James Bible. If you do that, make sure you reference every Bible you use.
- Your goal isn't to change hearts for Jesus (that can become preachy), but to tell a story that includes Jesus or religion. If you do it that way, it'll be the reader's own choice to find out more, not you pushing them to believe.
- I've found if one of my characters isn't religious for some reason but another one is, the belief of the non-believer is much more satisfying to the reader.
That's just a start for writing Christian romances. They're really fun to write, because the Good Guy always wins in the end.