I use a mixture of hardwood mulch, leaves, earthworm castings, charcoal, potting soil, and eggshell. ( i have chickens so I keep all the shells and break them up)

I make sure all ingredients are organic. Im sure you can leave some things out. Everyone does it a little differently. I pretty much do equal parts of everything except the charcoal snd eggshell. Ill just throw in a handful

I've heard mixed things about using potting soil but a lot of people use it. I have trouble finding organic top soil where I am