Okay that sounds fancy, but it basically is my diary of herbal medicine. I took a basic herbalist class, and have read several other books. In addition to this, my grandmother was a font of mountain remedies while she was alive. (picture granny on the beverly hillbillies.)
So the first thing I did was to find out what plants I have around me that have medicinal uses (be realistic. simple poultice/ tincture, not "can be made into cumadin.")
One great resource for this is GreenDean. If he does a weed walk near you, he will also talk a lot about whatever herbal plants he sees on the hike.
Anyway, once I had a list of the plants I have access to, I researched simple uses for them. I made a notebook listing the plant, what part of it is used, how it is used (tincture, tissane, poultice etc), what it is used for, what known dangers there are, and I included what books I have that reference this.
My herbal medicine book has about 40 pages. That isn't enough, or a lot, but I know and understand how to use every one of the herbs listed, and I know I have it in my immediate area.