I know that the final episode of the 7th season of Doctor Who, "The Name of The Doctor", which is supposed to answer many questions and address many hints dropped in the last 2 seasons, has been leaked. I don't want any spoilers, but I'm sure anyone who watched it must have walked away thinking "God, I wish I'd watched x,Y,z." What episodes do I have to watch to prepare?
I am not amongst those who have seen it already, but knowing what it's supposed to address, I think I would recommend the following:
The River Song Arc:
- "Silence in the Library"/"Forest of the Dead"
- "The Time of Angels"/"Flesh and Stone" [*]
- "The Pandorica Opens"/"The Big Bang" [*]
- "The Impossible Astronaut"/"The Day of the Moon"
- "A Good Man Goes to War"
- "Let's Kill Hitler"
- "The Wedding of River Song"
- "The Angels Take Manhattan" [*]
Items marked with a [*] are those I think are more likely to be optional. The rest I recommend because they either touch on the central mystery of the Doctor himself; or touch upon the "war" to prevent him ever getting to Trenzalore.
The Clara Oswald Arc:
- "Asylum of the Daleks"
- The rest of Season 7 part 2 (from "The Snowmen" forward).
Lastly, while I doubt they'll delve this far back, even in an anniversary year, the last two seasons of the Classic Series contain several episodes that attempted to set up a similar arc that sadly never played out because of the series' cancellation. There are actually quite a few resonances in Season 7 part 2 to this arc, but nothing very explicit. That said, if you have the time, you might find it interesting to see how an earlier generation envisioned playing out the Mystery of the Doctor concept.