I trained for my first marathon with Team In Training back in 2010. The key things I learned then (and since):
* Run with others if you can. Especially important on those long runs.
* Work your core. This is hard for me, but doing planks, crunches, and other exercises that work your core are really important on longer runs.
* Do long runs. I'd work up to several ~20 mile runs (no need to do the whole 26 miles, but the closer you can get, the better). For me, there's no substitute for moving on my feet for hours (however long it takes).
* Like any other running event, run your plan: don't ad-lib and change your pace.
* Do some agility training: skipping, heel running, toe running, side-stepping, etc.
* Learn how to run tired: if you can't do as many long runs as you'd like, do two shorter runs back-to-back (e.g., do a 10-mile run on Saturday and an 8-mile run on Sunday).
* Listen to your body: seriously, if something really hurts, don't push yourself, there'll be other marathons.
* Run with others if you can. Especially important on those long runs.
* Work your core. This is hard for me, but doing planks, crunches, and other exercises that work your core are really important on longer runs.
* Do long runs. I'd work up to several ~20 mile runs (no need to do the whole 26 miles, but the closer you can get, the better). For me, there's no substitute for moving on my feet for hours (however long it takes).
* Like any other running event, run your plan: don't ad-lib and change your pace.
* Do some agility training: skipping, heel running, toe running, side-stepping, etc.
* Learn how to run tired: if you can't do as many long runs as you'd like, do two shorter runs back-to-back (e.g., do a 10-mile run on Saturday and an 8-mile run on Sunday).
* Listen to your body: seriously, if something really hurts, don't push yourself, there'll be other marathons.
Good luck!