I'm no expert, but for my first marathon, I just cut back on the mileage (not the quality) the 2 weeks leading up to the marathon.   I was really sore after the last 20 and 22 milers and it gave me a chance to rebuild and get rid of all the little muscle aches going into the big day.   And now, this week is my 2nd and last week of taper before my first 50K, and I'm doing the same thing again. 

Both times I considered doing the cross-training thing during taper, but whenever I crank up a new activity, I always get more muscle aches, which defeats the purpose.   I guess I should probably do more cross-training throughout my training to prevent that from happening, but when I increase my mileage, I end up stopping any other activities. 

My only exception is yoga.  I have a teacher that incorporates a lot of running stretches for me, and it really, really helps me to loosen up.