Last year, I had a go at making leaf mould. Basically, you bung a load of fallen leaves into a plastioc bag, stick a load of holes in the bottom with a pencil and fill the bags up with water (basically so the leaves are damp in the bag). Then you leave the bags for about two years and hope that the leaves are turning into leaf mould.
I didn’t do it this year because I don’t really want yet more plastic bags cluttering up my front garden and I don’t yet know whether this will work. I did have a look inside one of the bags and it looks like it might be turning into leaf mould but isn’t quite there yet.
I think I have three bags of sycamore leaves and two of pine needles (supposedly, the pine needles make acidic leaf mould).