Lay a plank across the tops of the ceiling joists in your attic. Step only on the plank or on the tops of the joists. If you try to stand on the top of the ceiling, your foot will go through it.
Kneel on the plank, open a trash bag and scoop it into the cellulose insulation between two of the ceiling joists.
Hold the bag open with one hand and scoop more insulation into it using the dust pan in the other hand.
Fill up the bag but don't compress the insulation. Leave it loose in the bag so you can dump it back in place when you're done working in the attic. If you compress the insulation, it will lose some of its insulating value.
Scoop up as much insulation as you can with the dust pan. Remove the rest by sweeping it into the dust pan with a whisk broom and dumping it into a bag.