Use a box fan
Attach a HEPA filter to the intake side
Secure the filter with duct tape, bungee cords, or a cardboard frame
Make sure air flows through the filter before reaching the fan
Turn the fan on and run it in the room
Replace the filter when it becomes dirty
Use a MERV 13 furnace filter as an alternative
Build a Corsi-Rosenthal box with four filters, a box fan, and cardboard
Seal gaps around the filter edges to prevent bypass air
Place the purifier in a central, unobstructed location
Keep doors and windows closed while using it
Clean dust from the fan and surrounding area regularly