And don't put anything on in too large quantities....mix and match, grass clippings fine if interleaved with other stuff, mungle it up where you can, avoid twiggy stuff if possible but hey, you can always fish it out later, and as for couch grass, there is a real pleasure in pulling out those white devils from lovely brown compost if you've left the odd bit in! I love my compost heap, it's as much magic as seed germination is.
Oh, and you might get some nice surprises, I've had salad leaves, nasturtiums and even tomatoes appear on a heap....