Wouldn´t it be a nice idea to have a Read This First post on the top of this Forum, where you could provide answers to the most frequently asked question? Would prob. save a lot of time.
My suggestions to put into this list:
2)field values that you prepare in code will not be saved to the collection, you have to use setFieldValue()
3)if something runs in Preview Mode, but not in Published, check this, this and that