As a few others have mentioned, a blog hook is really important. Why should visitors come to your blog over all the 2 million other blogs just like it?
Activity is also really, really important. I've done many blogs with many different levels of activity and from different participants. The blogs that do the best (and are therefore worth your time and energy) are ones where you (or someone) posts every single day. I've tried to get away with weekly and/or monthly posts and heavily advertise "these are the days I post each month/week" and it has never done as well as daily.
I'd also recommend having a defined list of topics you cover. Will you post a weekly review? If so, pick a day of the week where you post reviews and stick to it. Perhaps you post a craft article on Mondays and have a guest blogger on Wednesdays. All of this gives your blog structure which readers seem to like and you'll like further down the road when you're having to figure out what to blog about seeing as how you've blogged every day for the last 437 days.
Find people who are dedicated to your cause...the blog. Use the blog as a promotional tool in that you offer a great blog that isn't all about you, you, you and your book, book, book. Offer something first. Something useful. Articles. Reviews. Recommendations. Occasionally mention you and your book. In other words, don't make every post and every square inch of screen real estate a promotion for your book.
Consider a smaller core group with open invitations to a larger group of authors. With a smaller core group you will have to post more often but you could perhaps have monthly guest columnists...people who have a standing date they show up to your blog with a post ready.
Start a schedule early and make sure all group members are aware of it.
Encourage group members to schedule (as in post to your blog) blog posts well in advance. This gives you flexibility and will ease stress in the long run.
Delegate. Have one person in charge of reviews. Another in charge of guest bloggers and so on.
I've been thinking more and more about the alliance Sandy mentions and they're a really great idea. I know of one group who does this and it's working out famously for them.
Hope that helps!
Ally