Share 'Read-a-longs'

Hi I'm thinking of doing a read-a-long on my blog and was wondering if someone could give me some tips on doing this successfully please? Do I talk about 1 or 2 chapters per week? How long do I leave for those who are interested in taking part, to get hold of the book that's being featured? Have you hosted a read-a-long? Was it successful or are there other blog features that might better to host…