Foreshadowing is one of the most valuable tools in a writer's tool box. It can be used to propel a story forward by hinting at possible outcomes, by offering tidbits regarding characters, and by building suspense. As the writer, you are in control of your story and your characters. By placing hints/clues to your story's outcome, you can manipulate your reader. You may choose to make your foreshadowing obvious. For example, if you wanted to show that your hero/heroine is headed for danger - you might put your character alone in an empty parking garage or having car trouble on a dark highway. But if you wanted to subtly hint at the oncoming danger, then you might mention a storm on the horizon or draw attention to an antique pistol on display. Either way works - it's up to you to decide which works best.