I usually start with a character. What if a man or woman heard or saw...?
I try to find the thing that character least needs or wants and slam that character into that difficult situation.
I might envision a situation and ask myself who would hate that situation the most. Guess who gets to work around that situation?
In Haunting Refrain William, a psychologist, doesn't believe in love or magic or ghosts. So I make him realize he loves his next door neighbor as more than a friend and she thinks she has ghosts in her attic and that he was her husband in another life. AND, to be mean, I give him memories of his life as her husband and on battlefields during the War of Northern Agression. (The US Civil war! )
In Protective Instincts I have a widow who is beginning to get back into like as she deals with her grief. What if someone is threatening her? What of someone wants to kill her? What if a man insists he needs to protect her?
Characters dive my plots, since I toss them into difficult situations. If a character is not ready for love, I make that person fall in love. I don't plot, but I know where each story begins and where I want it to end. Getting to the end is an adventure for me and for my characters. I write about the South and characters who believe the way I do, so I know what drives them.
Behavior which is normal and acceptable for a retired Marine would shock most other folks. So what if that Marine had to behave in a manner totally not his style? We love the "fish out of water" stories.