Speak to Lauranna Thar'well at Cenarion Refuge in Zangarmarsh. *WARNING!* You can only select one alchemy specialization.
My knowledge of alchemy is vast. It is, however, general in nature. If you wish to specialize, you will have to find others who have narrower fields of study.
If you wish to specialize in potion creation, I would recommend that you seek the help of Lauranna Thar'well of the Cenarion Expedition.
Her knowledge of plants will allow you to make the most of your raw materials. Look for her in Zangarmarsh and tell her I sent you to her.