Here’s what I do. Others may have helpful tidbits to add.

Skin head and remove everything you can. Cut out the muscle that holds the lower jaw in place and remove it, remove the eyes and as much “stuff” as you can.

Get a big pot of water and add some Dawn dish soap. I get that boiling on the stove, then transfer outside to the grill burner. Save propane and goes a little quicker. Caution… DO NOT boil in the house unless you want your wife to toss you out on your head. This process smells. Immerse skull to the rack line & Let the skull boil a while,(1 hr & check) Pick off any loose debris. Keep boiling and checking dependant upon how clean the skull is and whether the nasal bones start becoming loose. They will get loose, just don’t let them fall apart. This can take anywhere from 3-6 hrs for me.
Some guys on here use their wife’s roaster (wedding present) DO NOT EVER let her find out.

Power sprayer helps to get brain matter out clear the sinus cavity. ALWAYS KEEP MOUTH CLOSED DURING THIS STEP. Stuff shoots everywhere. Sometimes you can get everything with just a wire & a garden hose.

Once everything is free & clear, you can place on some paper towels in the sun to dry, or you can put on the peroxide paste from a hair salon. Some guys paint theirs too. DO NOT use bleach, it will degrade the skull over time and make it chalky.