Put on your dust mask, gloves and eye protection.
Measure the length of insulation you will need in the joist with your measuring tape.
Cut your insulation to the appropriate measured length with your utility knife.
Starting at one end, put up your insulation in between the joist. Put the flap of the kraft facing out over the wood on each side, and staple each side of the flap to the joist wood. Continue doing this all the way to the end of your length, staple every 3 inches on each side, or more if necessary to maintain proper hanging.
Continue to follow Steps 2 to 4 on each joist that you need to insulate. If you come to wiring that is blocking your joist or plumbing, it is best to keep the wiring or plumbing outside of the insulation. If you can't do this due to the wire or plumbing being too tight to the joist, you could stop the insulation at the wire or pipe and continue on the other side of it and stuff some insulation above the wiring or pipe by hand.