How to carry a MTB on one's backpack?
My friends and I have hiked a lot while carrying our bikes. What I've found that works best is:


go to the non drive side of the bike
drop the non drive side pedal down
left hand on the left fork lower
right hand on the non drive side crank arm
lift whole bike and place bottom tube behind your neck


This works because:


bike is central on top of you and you can easily remove one or both hands whenever necessary
you don't get dirty because the drive side is away from you


To lift the bike, your hands should go to the two red spots:



Also see How to shoulder a bike?