The questions to my answers can be found here: What Kind of Reader Are You? Part 1.
Sometimes I'll mentally list what books I need to read soon (within the next week or so), sometimes I'll decide while reading the current book that I want to read such and such book. And of course with series I have an idea of what I'll be reading soon.
I usually read one book at a time. Sometimes, I'll set one aside, read another, and then return to the first... if that counts as reading more than one.
I am a book hoarder and therefore, definitely have keepers. I don't understand people who don't re-read or keep at least some favorites on hand.
I usually finish the books I start. Sometimes I'll set them aside for a while and a few months later I'll restart and finish them. I do, rarely, not finish a book. Usually if it's school related or if it's very depressing. (I never finished A Thousand Splendid Suns, for instance.)
I do prefer to read series in order. If I can, I'll usually read them one after the other. For various reasons, this isn't always possible.
I'm an "average" reader, but I have trouble leaving a book before it's finished so I usually finish a book the same day I start reading it. I'll lose sleep to manage this time-wise.
I pick up a book whenever I have time available and usually, but not always, have a book on hand.