Split Screen/Picture-in-Picture Technique...

Our group got told about this interesting concept that is used in the film '500 Days Of Summer' to show the character's reality alongside the character's expectations. We could possibly use this technique in our own film opening to show what really happened to our main character (or our main character's friends) the night before alongside what our main character wished had happened.
Here is a simple video on how to create this Picture-in-Picture technique on iMovie;