Decide what you are going to write about; a whodunnit or a romantic chicklit story.
You whodunnit/thriller could start with a strange disappearance or unexplained murder.
Your chicklit could start with a surprise visit or mysterious person.
First, write a short outline. Include the following information for your story:
1. Who is the main character/suspect? And who else are involved?
2. What happened?
3. Where and when did it take place?
4. Which possible explanations are there for the whodunnit/which different scenarios are possible for the romantic story?