Lots of good stuff in this thread. But I'm going to tell you how I plan too just so you have a variety of opinions.
I already have certain meet ups planned that aren't officially SDCC. These are usually the forum related meet ups that are the same every year. Then I start filling out my schedule around those as studios and individual panelists announce things. Panel confirmations are going out to panelists right now, so things will start getting out there pretty soon as individuals start to talk about their own panels online. Studios will also be making their own announcements.
However, since the schedule doesn't come out until two weeks prior, all of this is tentative. Then when the panel schedule gets officially released I lock everything into place.
Unlike a lot of people, I don't usually have a back up plan. I usually put a great deal of effort into making my schedule stick. But that's just me being an anxious person who hates change haha.