I recently moved away from DC but before that was in a book club that had been going strong since 2004. We just had our 50th meeting a few months ago. It is still going strong now too even though I'm gone (sniff sniff!).
It started off as a group of girls that all worked together but as well all moved to different jobs we brought in more girls which helped to have a bigger group and kept us from always ending up talking about work. We found that having 10-12 girls on the "roster" was good since inevitably people couldn't make it and we usually had about 8 people attend.
We initially started off with the idea of doing it during the week at a restaurant but very quickly evolved to doing it on a Sunday around noon at someone's house with it being a potluck. It actually was a lot of fun to host and if you have about 10-12 people then you really only host like once every year or two. Our group lived all over the DC area as well so we tried to get a good rotation going between DC, MD, and VA so that we were not always going to one spot.
We aimed to meet every 6 weeks or so depending on holidays/busy times etc. We generally did not go longer than 2 months but also didn't really go shorter than one month so that there was time to read.
As far as picking the book, we started off with the hostess selecting the book. But after a few really bad picks that no one ended up finishing, we started a voting system. During book club we would figure out who was due to host next (it was not an exact science but we more or less had a rotation so we knew when our turn was coming up) and that person would send an email shortly afterwards with 2 or 3 date choices and 2 or 3 book choices. Everyone would then vote on the date and book and the majority won. We found that offering a few dates worked well because for the most part it was usually evident if one date would be horrible and the other would work for most. Voting on the book helped so that if it sucked then we couldn't complain!
We liked to try to find books that either had book club questions at the end of them or questions that could be found online. That at least gave us some stuff to discuss before we went off topic

There are a lot of book club websites with suggestions for books as well. We also like to try to pick books set in other countries so we could have a food theme for the potluck! We did several meetings at the Teaism in Penn Quarter if someone had a small studio apt and couldn't have us all over!
Also, several of the books we read ended up being made into movies so we did several movies dates as well.
Off the top of my head here are a few books that we read (some are dated since we read them years ago!):
The Little Chinese Seamstress (Chinese food)
Confederacy of Dunces (Louisiana food)
The Kite Runner
Never Let Me Go (fascinating discussion and now a movie)
Into the Wild
Suite Francaise (French food)
My Name is Light (Argentina food)
Kafka on the Shore (did a tea at Teasism)
Night
The Space Between Us
The Man Who Mistook his Wife for a Hate
The Virgin Suicides
Atonement
The Shadow of the Wind (Spanish food)
Eat Pray Love (italian/indian food)
The Bastard of Istanbul (turkish food)
The Yiddish Policeman's Union
The Time Traveler's Wife
The Bonesetter's Daughter (chinese food)
The Persistence of Memory (south african food)
My Name is Red (turkish food)
White Teeth
Of Love and Other Demons (latin american food)
Miguel Street
Corelli's Mandolin
Holly Cow (indian food)