1. Personal Safety: Wear goggles and a gas mask to prevent dirt, dust and biologically hazardous fumes from coating your eyes, mouth and lungs. When you start cleaning a place like that, many different cruddy things get stirred up into the air that you're trying breathe and see through. I wouldn't want you to get an eye or respiratory infection.
2. Take a broom and sweep all the cobwebs, dust and hair from the ceilings, walls and baseboards. If he has central air, turn the fan to the [on] position rather than leaving it on [auto]. Apply this setting temporarily until you have all this airborn solid crud matter filtered through the furnace filter. Then you can simply dispose the filter into a solid waste container rather than polluting the neighborhood with his crud as a result of opening all the windows. Plus it's a hassle to have to remove window screens to spray them down from all that grime collecting on them and then having to wrestle with putting them back in place. If he doesn't have central air, just let the dust settle for about an hour after you're done sweeping down the ceilings, walls and baseboards.
3. Vacuum all rugs and carpeting, then use an electric vacuum sweeper on hard floor surfaces to prevent the crud from being stirred back up into the air. Then turn the furnace fan back to the [auto] position if applicable.
4. Wash all of the walls and ceilings down with a premixed, no rinse formula of TSP (trisodium phosphate). This is an inexpensive chemical cleaner that you can find in the paint department at your local hardware store. It's what the pros use to prepare surfaces to be painted. And it's a heavy duty cleaner that works better than anything else you can find on the market.
5. Use a spray-on bleach cleaner such as Clorox® Cleanup® to clean, disinfect and deodorize his kitchen and bathroom.
6. Take a shower to remove all that cheesy goo that will be coated all over your skin and hair.
If none of these procedures work, call your local EPA to have his dwelling evaluated for the consideration of being condemned for health safety risk violations.