You need mortar and pestle. Do this in a place indoors (homes, stores, etc).

You have to be patient. You also have to know the duplication glitch.

Get any two foods, for example apple and pear. Then use the duplication glitch on both of the fruit.

Try to make at least 200 of each. Keep picking them up even if you are over encumbered, now use use mortar and pestle and keep making potions no matter what cause they make.

As you make them your alchemy skill will go up, when you are done all you have to do is drop the potions and if you want, do it all over again.