Experiment with things that are outside your comfort zone. Try writing from a different POV. First person, third person, past, present, alternating POV by chapter, changing POV, writing stream of consciousness which is the one that really really gets into the character's head because you 'are' the character, telling things exactly as they happen.
Don't think of a story, let it come to you. Live with the characters and Mike said. For the time you are writing 'be' them. Let them speak to you, interact and provide you with dialogue and take your story in different ways. With some of my stories the route the plot has taken has totally shocked me because it is very idfferent to what i had intended. Let yours do the same.
Try planning and researching.
Try mapping out the whole story, loosely or chapter by chapter
Try writing with no idea where the story is going just letting it take you.
Write as if they are journal entries or with an outside force dipping in and commenting or as blogs or anything at all that takes your fancy
Try anything you can think of that is new and you haven't done before.
Most of all have fun.