I have long been of the opinion that if I get through the first quarter of a book and I can't think of a single character that I care about I should stop reading. (Although, in practice I usually finish any book I start) One of the things that I have found is that when I'm reading good authors I find myself having imaginary conversations with them. Telling them about the one piece of information they are missing, or how that other character really feels, etc. My favorite example of this is Lois McMaster Bujold's Vorkosigan's saga. I have been through those books over & over again. I still find myself talking to Miles (the MC) and will still tear up over certain passages. So what do YOU do to make people actually care about your characters?