Potion making is notorious for being a difficult skill to level, so the honest answer is, there is no really quick way to do rank D training. And don't hold your breath on getting rank B... rank C has the same goals as D, just rehashed.
The key is going to be getting storage space available to you. Lots and lots of storage space. Stockpile herbs and wait until Monday. Watch the
weather for category 7-9 storms or thunderstorms. And above all, try to party with fellow potion makers. This will ensure that your hard-won herbs do not go to waste [as much].
As for getting the goals completed, wound healers will give you the fastest xp, but that necessitates that you have a significant amount of inventory space. No matter what you focus on, however, you
will have to do a minimum of half of the total requirement of wound healers for rank D in order to break 100 skill proficiency. There's simply no way around it.
If you have the cash and time to spend with an herb pig, I highly recommend using one to supplement the herbs you get from dungeons. As an added bonus, you can use the hpmp30s you create for potion making xp to replenish its mp supply and get more herbs. And always take some time to browse player shops for deals and/or reasonable prices for stacks of herbs.