is there a trick to build a compost bin?

What's actually going wrong, smell or nothing breaking down? The bin itself can be four pallets screwed into a square, open bottom on bare soil. Getting it to rot is about the mix. Roughly equal volumes of greens (veg scraps, grass) and browns (cardboard, dry leaves, shredded paper). Slimy and smelly means too much green, add brown. Dry and nothing happening means too much brown or it needs water - it should feel like a wrung-out sponge. Turn it every couple of weeks if you can be bothered.