Clear the workspace and cover the furniture and floor in the room below with a drop cloth.
In the attic, roll the insulation back just so that it's out of the way. Later you'll roll the insulation back into place. Measure the space between the joists.
When working in a hot attic, make sure to drink plenty of water and take frequent breaks. It also helps to work early in the morning when the temperature isn't as high.
Measure and cut the wooden boards to size. Don't force the blocks into place. That could put more pressure on the ceiling joists and could force them to move over time. Cut down the boards if necessary. Lay each board flat against the ceiling and screw into place.