[MadMax]

Start with a shopvac with a brush nozzle end..should deal with most of your problems. Blowing air through it from the back side will get stuff loose too. Then just wipe it down with a damp cloth. I also cleaned all around the edges and lips, even on the glass. Mildew will build up in there, and stink up the opening...nice and fresh will make it more inviting to open.

 

[MadMax]

Dealership has a service to clean the evaporator...it's usually around $80, I did mine and it smells so much better! Not new car smell, but no more must. It was worst when the car would sit in the sun for a few hours and you first get inside...turning on AC of course only made it worse for a few minutes, eventually would get reasonable.