When you're writing and you're in the zone, you just write. Everything is flowing perfectly. And then it happens... you hit a wall. Where do you go from there? How do you move on to the next scene?
For some, its as easy as taking a break and starting again after eating, or drinking, or taking a walk. Some have more difficulty trying to decide what should happen.
For me, everytime I start a scene I ask myself two simple questions. How are the characters going to react to this? and How will my characters resond?
Everything in a story comes down to actions and reactions. When one character screams "OUCH!" another character asks them why they did that. When one character pushes another, that other character reacts accordingly. Unfortunately, this sometimes means jumping into several different heads in succession. Trust me, it can give you a headache.
You can practice writing this way as well. Make a list of situations--some ordinary, some anything but. After that, get your list of characters and answer each situation with how that character would react or respond to it. It tells you a lot about your characters, not to mention it can help you out later in your story when those situations arise (if they do).