This post is for Cheryl, who asked.
There are a finite number of plots. This is especially true of novels set in the Regency, restricted as they are by the social mores of the era and the expectations of contemporary readers. (I sometimes wonder what Georgette Heyer would think of what ‘Regency’ has become; whether she would be amused, amazed, or appalled.)
It’s a fairly safe bet that whatever your theme is, it’s been dealt with before. You need to determine what makes your version different from the rest. What about your hero is unusual? Making him the most handsome alpha male to ever set foot on earth isn’t enough. He can be a charming rogue, a brooding introvert, a remorseless reprobate who redeems himself, or anything in between; but whatever he is, the reader needs to connect emotionally with him. Decide what elevates him above the average romantic hero.
Do the same for your heroine. If she’s a virgin — I am so very tired of wide-eyed virgins — please, please give her some personality.
Separating the hero and heroine for a fair chunk of the story is a plot device I personally dislike. It does provide an opportunity for some fairly intense character development, however. Think about how to make the best use of this. Make a point of not doing what everyone else has done, which usually involves considerable angst on both characters’ parts. (This is the part of a book than I usually skim, wanting to get to the point when the hero and heroine are together again and we can get on with the tale.)
Local color can be helpful. Readers are interested in places they haven’t visited before. Quirky secondary characters and subplots are fun. Just be careful not to overdo. You don’t want to detract from your main story, or slow down the narrative flow.
I used to look for what I thought of as ‘hooks’, interesting and relatively unknown things that would give a story what in the film biz is known as ‘production value’. I’ve used tinkers, newspaper publishing, Bow Street, ghosts, missing relatives, stolen jewels, runaways, kidnappings, murders, details of servants’ lives. Most of all, I’ve used humor, but that’s not for everyone.
Characterization is — in my opinion — the key to a good story. If your characters are vivid and involving, it doesn’t matter if you’re working with Regency theme # thus-and-so. Your characters will make your story different from any told before.
Don’t struggle with the problem. Sit down with your story and let your characters tell you what to do.