@joygirl: I think it terms of cities it's always a good idea to have a key part happening in the grimiest part where the people in charge don't give a damn about the people living there. Maybe due to the alien thingy slavery has started again?
@joygirl: An example would be for number 18 a car crash happens and at number 19 the main characters best friend is eaten. Maybe because of the car crash he was in a coma for a week and he wasn't around to help his friend ETC.
I couldn't be bothered to read every post in this thread but how I would go about it is by writing 20-50 things down that are going to happen, they can be major or minor. Put them in the order of how you want them and then all you have to do is figure out your going to get from number 17-18 etc.