I have cleaned up after a fire in the area and learned a few things the hard way, so if anyone in SoCal is reading take note.
If you have wood ash, from trees or lumber, you need to use a little caution. Your regular vacuum is not designed for this stuff and will create a breathing hazard if you use it. Wood ash is alkaline. The easiest way to make lye is putting wood ash in water. It has a pH of about 11, just a little lower than household ammonia so it is important to clean it up. Wood ash also contains some super fine particles that will pass through a normal vacuum cleaner filter. If you use a regular vacuum to clean it up you will fill the air with superfine caustic dust that does not do good things to your lungs.
You need a vacuum with a HEPA filter. Many vacuums today have them, but I use a 10 gallon Shop Vac because it has a plastic tank and the standard sheetrock filter [an extra cost option] does the job. Sheet rock dust is just as fine and many of the filters mention their HEPA compliance.
Wash your clothes and self with plain water first to get rid of the dust. Regular hand soap has a pH of around 10 because it is made with lye, so you don’t want to over do it.
Wear a good mask, goggles, and gloves when you are cleaning to avoid problems. You can wash the ash into the soil outside, but it will make the soil more alkaline. Avoid getting this stuff in storm drains, because it can clog them, especially in areas that don’t get a lot of rain. If you are subject to acid rain, it will help the soil, but it can cause health problems, so you have to deal with it.
If you are cleaning with a damp cloth, a little lemon juice or white vinegar in the water wouldn’t hurt, but don’t get carried away.
Update: Do not even consider turning on a leaf blower, OK, and pay attention to the exhaust on the vacuum cleaner. You do not want ash in the air people and animals breathe.