Recovery after long ride I biked the longest I have in my life; my previous record was one 12 mile ride, but today I went ~36 miles on my MTB. Should there be any steps I take to recover myself? Also what things should I inspect on the MTB? I noticed that during my ride there was sometimes pain in my lower back ... should I be moving the seat forward or backward?
You cannot draw any conclusions from one ride. Especially when your have ridden triple the distance of your previous longest ride. Anyone would expect some discomfort in that situation.

Regarding recovery, it should have started during the ride. By this I mean you should have made sure you ate periodically and drank frequently. Some things that can help recovery


a massage by a sport masseur
catching up on fluids
a good meal
a good sleep
a recovery ride
stretches before your muscles cool completely
and (I previously omitted) a cool-down period before you stop exercising. 
also, sports compression garments (especially shorts in this case) will help your muscles recover.