Work in some well rotted manure. Cover with a thick layer of fallen leaves in the Fall, let it compost down all winter. Turn it all under in the Spring before sowing.

I would uncover it and sow a crop of green manure - you'll be able to buy the seeds at a good nursery. Alfalfa is one sometimes used. Then before it flowers dig it all in.

If you live near a farm or a riding stable you can often get a load of manure though sometimes you have to take bags and shovel it yourself. If it's well rotted you can spread it and dig it in, but if its fresh it needs leaving in a heap to rot down before spreading.

You might still be able to find some plants of purple sprouting broccoli that you can grow over the winter, though its a bit late. But in late autumn you can sow broad beans if you live in a fairly mild district - unfortunately you didn't add your county to your profile .
You can grow them successfully under a polythene tunnel and they will be ready well before spring sown ones and even if the beans aren't brilliant you can make a good soup with the young pods alone. . Aquadulce is the best variety for that. When they are finished leave the roots in the ground because they have nitrogen nodules on them which will fertilise the soil.
For more suggestions see egThompson and Morgans suggestions of what can be sown now. It is better to have plants growing than leaving the ground bare and covered.

Start a compost heap for all waste plant material - you can bring it from your kitchen too (but nothing cooked)