I have made potions for a number of years now and the trick is to know your ingredients and So your first question would be as in any sort of magick what is your goal?
So you know what you are going to make what are the herbs you will use in the potion? Before you make something like a tea or a tincture know that some of the herbs used in potions are poisonous I have ingested some of these as it important for me to know the side effects (I do not endorse this method as it can lead to very uncomfortable situation or possibly death).
Also some herbs will not go together and you may have yourself something that doesn not smell so great.
Second question what are you going to use as your base are you making a brew? a magick oil? a tincture? Ink?
The most common of potions are brews (teas) and oils, not many these days know how to make a proper tinture or how to make a proper Ink.
Brews-your going to need either a tea ball or you could learn to read tea leaves your choice most days I prefer a tea ball
Oils- Olive oil is really the best for this it is what is called a carrier oil meaning that it will absorbe the essense of the herb easily, baby oil is not recommended at all.
Tincture - this is made with alcohol, i prefer vodka because it is a clear alcohol with out much of a sent and taste of its own and will not mask the the herbs own sent and taste.
Ink - try to get a rubbing alcohol for this and remember that if you do not add arabic gum your inks will be very very runny and will not be very good for any sort of quill.
For a guide for your herbal ingredients a book like Scott Cunninghams Encyclopiedia of magical herbs is an excellent one
This may also be of some help to you
http://www.scribd.com/doc/2579970/Herbal-Magick-A-Witchs-Guide-to-Herbal-Enchantments-Folklore-and-Divinations-Scolder
