Look up how to prepare herbs, from infusions to decoctions, salves to poultices,
Learn the words used to describe herbs and their functions. What is a contraindication? What does a nervine do, an antiseptic, an antispasmotic, a diaphoretic.
Understand that herbalism is NOT like western medicine. We cure by creating balance in the body, not by putting a bandaid on the wound. You need to know how the body works.
Then you need to begin learning about your herbs. Pick a common one first and research it until you're just coming up with repeatitive information. I started out with researching ailments that I or my family had as well as wound care. Herbs that would be useful and utilized.
Once you get an idea of how herbs work and what constituents within them make them work, you'll learn how to recognize those properties in other herbs. For instance, tannins heal burns and stop bleeding. They are normally wherever antioxidants are found, and they are astringents. They are what makes the skin in your mouth feel tight, like when you eat blueberries or drink black tea. Many things contain tannins, some more than others. One day about 7 years ago, I burned myself badly on a light bulb and nothing would relieve the pain. It was mostly 2nd degree and about a 1/8th inch size 3rd degree portion. The 2nd degree was the one hurting (3rd degree doesn't hurt), and the 3rd degree section was too small and minor (white skin) for me to be concerned with. It was late (hence why I was using artificial light to see) and stores weren't open and I was visiting a friend and staying over. Sooo, I grabbed a black tea bag, wet it well, lined it up with the burn and then wrapped my hand in a ripped strip of cotton cloth. 45min later, you couldn't tell I had been burned and neither could I. The 3rd degree section never scarred either.
If I didn't know what tannins do and what has tannins, I would never have thought to use black tea. You won't find that remedy in a book, and the ones online are most likely written by a lady named WhiteRaven or anonymous from Chicago, IL. So learn your constituents and what has them! ;-)
Since you are interested in Herbalism you may consider taking a herbology course as there is a lot of information you will learn about herbs. I would also suggest the book Today's Herbal Health: The Essential Reference Guide by Louise Tenney. It lists the herbs, what they are good for and much more information. I have used this book for years and always use it as a reference whenever I make herbal remedies.
I suggest the Encyclopedia of Magical Herbs and Magical Herbalism. Both are by Scott Cunningham. I also suggest P.D.R for Herbal Medicines First Edition, which is a book, compiled of medicinal herbs. I personally own all three of these books and they are very valuable resources for herbalists. I also suggest you look at this man's herbalism series on Youtube.
http://www.youtube.com/playlist?list=PLF15749FA23620164&feature=plcp
Start with researching. Research is VERY important as some herbs can be toxic if not used correctly. Every herb you use you should know a good amount about.
Theres a lot of sites that offer information on herbalism, this one does as well. Theres also a good amount of books out there. Herbal work is a pretty intensive thing and it may take a while to could do all the research but keep working at it. I enjoy it a lot myself.