Write down reactions to these events in your character's voice. Think about what events led to his walking down a French village street, or why she is standing on the beach, crying. Is she so wrapped up in her own sorrow that she has shut out the other beachgoers and doesn't even realize she's not alone? Or does her crying make her self-conscious, trying to discreetly dab away her tears before someone notices?
Thinking as your character, test your reaction to an imagined predicament and the factors that brought you to that particular time and place. Stage a conversation between your character and an antagonist. Try a fifteen-minute freewriting exercise, writing in your character's voice. Immerse yourself as deeply into your character as an actor does just before he steps onto the stage. You want to make sure each character carries his or her own weight, and that you wring every drop of emotion and complexity from their respective stories. You can't do it convincingly if you can't think like they do.
Of course, when you learn the knack of slipping into your character's head, you might find your story line taking off in a completely different direction than you'd planned--one dictated by your characters. Go with it. It might be different than what you had outlined, but it will probably be more intriguing. Often, your characters are better judges of how things should play out than you are.
When you live inside your characters' heads day in and day out for months, they become an integral part of your life. I think that's one reason authors feel a sense of loss when they finally pack up their manuscript to mail to New York They've been inside their characters for so long, so intimately involved with their every thought and move, that when they ship them out the door, they feel the way a parent does when a child finally moves away from home--a bittersweet blend of happiness and solitude.
The novelist E.L. Doctorow said, "Writing is a socially acceptable form of schizophrenia." Let yourself go. Your writing will be better for it, and you'll create characters your readers won't soon forget.