Mostly I read new things, sometimes I re-read old classics, and just occasionally I get fed up with trying to read "good" books and go back to some indulgence from the past. It's always so fascinating to see how differently you re-read a book, and what you notice that you didn't see the first time round... and why.
I first read "Foundation", Asimov's history of the reconstruction of an entire galactic empire, when I was seventeen. The most notable thing for me though, on re-reading? Thousands of years into the future, and amongst the many politicians, traders, members of the military, priests and academics we meet in the book, not one is a woman. In fact the only female character in this entire century-spanning book is an evil queen who is distracted with extraordinary rapidity by some nice shiny jewelery.
It dates the book so particularly in time, for me as a reader. God only knows why I didn't notice any of this the first time round, as my reading of it definitely post-dated Star Wars with the bolshy and adorable Princess Leia. And how extraordinary that Asimov himself never thought to wonder whether, even in the very near future, world power might be slightly more shared between the sexes than it clearly was in his day.