Flatten the weeds, but don't cut or pull them. They will become garden mulch. Sprinkle a thin layer of high-nitrogen manure over the flattened weeds.
Cover the area with sheets of organic material. Cardboard and newspaper are good options. Overlap the sheets so that the weeds don't find a way from under them. Lack of light will kill them.
Top your organic cover with a 10-cm layer of partly rotted manure or compost that's free of weed roots and seeds.
Pierce the mulch, and make a hole in the ground. Plant your crop. Seedlings, which birds and other animals often eat, will be more successful than seeds. When you're opening up new ground for your first permaculture crop, potatoes, corn and plants in the cabbage family are good choices. The following year, you can plant anything that grows in your climate.
Water the plants well but not the mulch in between them. Since mulch holds on to moisture, it's possible this is the only time you'll have to water your garden, unless the weather is extremely dry.
Cover the bed with a 20-cm layer of straw, grass clippings or tree leaves. Arrange them around seedlings so that they can poke through. Cover any root vegetables that haven't germinated. If it's been raining or you live in an area of high humidity, don't complete this step until your plants are big enough to survive a slug attack.