I'll echo a lot of what has already been said.  Hal Higdon is a good step up from Galloway; in addition to Higdon's book, he has a website that has a wealth of information and training plans available for free.

I broke 4 hours in my second full.  I ran my first in 4:16 after about of year of running with any sort of serious application.  (I had about a year and a half of three mile  runs ten to twelve times a month, but I was in decent but not great shape when I started training seriously). I ran my first with no real goal time and the intention of having a good time. I strongly encourage this approach for a first full.  But once I knew I could run a marathon, I wanted to improve, so as I built a base and ran over the year between marathons, I worked on racing and learning how to race.  In my second full, I had a plan and knew the course, and it worked out perfectly; I missed my total reach goal by less than 2 minutes and ran a 30-minute PR.  I'll be running #3 and probably #4 this year, with a goal of going under 3:30.

FWIW, I still haven't managed to average over 30mpw for anything longer than a two month stretch (I had a series of stupid, non-running injuries last year), and I still don't do any regular speedwork.  Hopefully both will change this year.  So I don't suggest you try to do what I have been doing in that regard.

I think the moral of the stories our collective running progressions is that marathoning is a journey and an is also experiment of one.  The latter is what makes it so maddening, but both are what makes so enjoyable, too, so enjoy the journey.  In the end, the accomplishment and the thrill of the well-run race is what gets you out the door when you're tired, when it is freezing cold and dark, or out of bed in the early dawn of a muggy summer morning.

So, welcome to the group, stick around, and join in our daily chat threads.  Ask questions; most of us have learned what we know the hard way, so we're happy to share.  We're not a super-secret conclave, we just like to chit-chat more than the main boards here at RA are really used to.