When I worked in a papermill, even though we were an entirely machine-made mill, most of the questions we got from local schools were about how to make paper by hand, or how to make recycled paper.
This Instructable however, will cover the manufacture of paper from virgin fibres, that is, from plant to paper with no recycling, using a mixture of vaguely-traditional techniques from the European and Japanese papermaking styles. The final paper will probably be best classified as a "craft paper", suitable for scrapbooking or for card making.
The plant in question: the common stinging nettle (Urtica dioica), so you have the added attraction of being able to use the left over leaves for brewing nettle beer, or making nettle tea or nettle soup.
You could also use similar processes to make paper from plants like flax, jute or hemp.
Step 1: Raw materials
I collected a large carrier-bag full of nettles of a mixture of ages, from fresh growth to mature plants.
Long sleeves, gloves, even hat and eye-protection are all useful here, depending on how energetically you harvest the crop. The worst sting I got preparing this Instructable was through the knee of my jeans, but most parts of me got lightly stung, even through gloves.