Mixing in grass clippings is a great help. I've got a big bin of leaves, over the next few months I aim to mix in as much grass as possible. Basically by turning it into the next bin, a layer at a time and mixing well. Probably do that twice and then leave it. In one year, I get very good results. The forking about helps break it all up. This is in a wooden bin, covered with a plastic sack. (But I'd definitely leave the lid off the dalek.) It's like a lot of things, if you've got the time, space and energy, you can work wonders.