Notice how you already use first person narrative in your daily life. When you tell your friend, "I went to the store today and got caught in a rainstorm," you're telling her what happened from your point of view -- that's first person. Write your story in the same fashion.
Study romance novels written in first person. Read books by Victoria Holt, Phyllis A. Whitney and other romance novelists who implement first person point of view to tell their stories. Read mystery novels as well -- many of them, especially cozies, are written with a first person narrative.
Write a character sketch of your heroine. Make it as long or as short as you need to really delve into her mind and emotions. Let her tell her own story about her family life, her likes and dislikes, her hopes and fears and how she feels about the hero of the story.
Imagine yourself in your heroine's position. What would you do if your house burned down, you lost your best friend or met the man of your dreams when you looked like a train wreck? Imagine the emotions that might accompany the events your heroine experiences and weave them into your novel. Make it easy for your readers to put themselves in her place and identify with her.
Create a rough outline of your novel from your heroine's point of view. You can use one sentence or 10 pages, whatever it takes to get your idea on paper. Realize that your outline may change numerous times before you reach the end of your novel. Your outline is simply your guide to move your character from one point to the next.
Set a regular writing schedule and stick to it. Look forward to spending time with your heroine, her friends, her family and her hero. Make every word of your story count and live vicariously through your heroine so you can tell the tale from her point of view.