It all depends on where you live. I would suggest studying and reading. Looking into records of the natives an the medicine an plants they used in lore. I would also suggest reading some books on herbology. I'm into herbs right now as well, and like many of the topics regarding the occult/magik it can be difficult.
I thought learning herbs was going to be an easy affair. But beware, there are so many cousin an sister plants, That will have or not have stronger effects. For example I was also looking for herbs, I told a friend I was looking for wormwood. He then told me it grows in the wild where I live. So I found someone, researched it and then found out it was not the REAL wormwood but a cousin of the same specieies. Thus not having the same effects an properities.
This topic is a fascinating one to say the least, but you are constantly learning and researching. It takes alot of work. I also suggest finding other herbalists in your community who can teach you as well. You can also make friends around the world who have plants growing in abundance and do trades via mail. Sometimes they will mail you some for free.
Another suggestion is there maybe more but two stages of herbalilsim I no of. Such as magikal uses of plants and then medicinal. Pick one learn as much as possible then move on to the next. Its confusing if you do both at the same time. I do have a vast collection of 160 books and some of these books are on herbs. If you want some of these books shoot me a message and Ill reply with them via mail on spells of magic.