Each herb works as a physical embodiment of One's Will (if one fully understands the context and application of that herb, root, resin, or substance). There are dozens, if not hundreds of books that one can find which will provide proper guidance in this matter (I personally recommend Cunningham's works, as that he provides an extensive treatment of most commonly used herbs, their historical associations, and mystical properties).
However, if you can't afford to make your library flush with such books, here is a brief collection of information relating to Herbal Craft that I have gathered. Of course, this is far from an extensive list, but it is something that can get you started
The beauty of using herbs is that once you realize that they DO possess a physical representation of one's Will or Intent (if so applied), one will immediately recognize the usefulness of such lists when performing such simple acts as COOKING. These herbs can also be combined together to make powerful incenses. Generally, when making incenses, I look for three herbs that are complimentary and can be built upon each other, thus "Stacking" the effect threefold.
If you want to make a real "Slam Dunk" incense, seek seven herbs with common properties use a mortar to grind them down (separately), placing each component within a clean bowl, and then combine the completed work together in the mortar once more, grinding them together while focusing your will upon our work (new users will find this VERY taxing if they are doing it correctly, because of the amount of energy being drawn from yourself and placed within he mixture -- it does get easier over time, but be warned, it is best to do this when you are WELL RESTED, even if you are an experienced practitioner). Once complete, consecrate the work (meaning set your new incense powder to a SPECIFIC purpose), and place it within a fresh container (I like using those plastic Rubbermaid containers that you can get in groups of six or so -- they are cheap and air tight!)
You now have created a real live and wholly effective incense! Some people like to use a resin or gum to form it into cones or sticks. I prefer to keep it as a powder, as that it burns more cleanly and as you add it to your coals, you can place an invocation upon each small spoon full (or in my case I use my Athame to draw out small portions to place upon the flame -- the Athame is a symbol of Air and thus THOUGHT, it seems wholly appropriate to utilize this instrument as an extension of my own THOUGHT-FORMS as I place the incense upon the coals).
Well that's enough for now ...
p.s. Keep in mind that while SOME of these herbs, resins, and roots CAN be consumed, I would advise against it unless you are certain that it is safe. Basically, a good rule of sense would be if you can purchase it in your local grocery store to season food, you probably can eat it!