I started running in Jan 2012, and ran my first marathon in April 2013 (OKC Memorial Marathon). I ran some of my long runs with my bff, and her pace was about 3 mins per mile slower than mine; I don't know if that had an impact. I also weighed about 8-10lbs more than I do now.
I started doing weekly sprints on the treadmill in May; I definitely think that has had an impact on my overall speed. Everyone told me that this marathon is super hilly, so I added hills into the latter half of my longest mid-week run (treadmill). I cut out sprints during the taper though, and didn't do any hills last Tuesday. I think part of the improvement is simply that I've been running a teensy bit longer; some of it is surely stubbornness. The memorial marathon was my 6th race; today's marathon was my 16th race (various distances; this was my 2nd marathon), so knowing what to expect in a race and being a little bit tougher mentally probably helped. I definitely do not expect to have this big of a PR ever again. I was probably more aggressive in training than I should have been-I haven't even been running for 2 years. I paid for it, too: I had shin splint issues for most of the summer, and my IT bands give me some problems if I'm not diligent about foam rolling.
If I pick a time goal over less walking breaks as my goal for the next marathon, I doubt that I'll have anything better than a 10-15 min PR at the most. I really need to take a few weeks off from running and let my body recover. I think that how well I can recover will dictate how my next training plan will go. I'm not the best at taking rest days, but I think I can be disciplined enough now to recover properly.
That's awesome!
Oh, and I switched from Brooks Glycerin 10s to Pureflow2. I did it gradually over the month of June.