I'm sure many of you have figured out how to level your Herbalism already :) I really should have posted sooner since I actually capped on Day 1, but with so many other things going on it got pushed to the back burner. The first thing I want to recommend is a pair of +5 herbalism gloves. You can purchase plain white gloves from an armor vendor in any major city and enchant them. They won't be soulbound, so you can mail them to an alt when you're done. This may seem like a strange suggestion since Goldclover (the first Northrend herb) is yellow at 375. The gloves aren't for the clover, they are so you can move up the chain quicker. While Goldclover is certainly a useful herb, no one wants to hang out in noob zones any more than necessary.
Your first goal starting out will be to reach 400 so you can unlock other herbs. I prefer Howling Fjord for Goldclover farming, since it tends to be a bit less crowded and there are actually more herbs there compared to Borean Tundra. If you are just not finding Goldclover, another option is to farm Firethorn in Borean Tundra. Firethorn spawn around the Geyser Fields and while there's not mass quantities, it's also not a terribly popular item. I regularly see Firethorn just laying around, so if you're desperate for skill-ups you can fall back on that.
Frozen Herb used to require 415 skill but I believe it's been changed to 385. Unfortunately there's not a lot of Frozen Herb spawns in Dragonblight so I hesitate to recommend that as a farming spot. Talandra's Rose is also unlocked at 385, but it's found predominantly in Zul'Drak. If you can't traverse Zul'Drak safely, you probably shouldn't include the Rose in your plan either. The path I used with my level 70 hunter was to get to 395 (+5 gloves) and then go to Sholazar Basin. There is Goldclover, Adder's Tongue and Tiger Lily there. If you're careful of the mobs, you can safely herb certain areas. The southern border is fairly safe, the central area near River's Heart has lots of Tiger Lily spawns. You can also do laps around the Rainspeaker Canopy (just NE of River's Heart) and dodge the mobs there pretty easily.
If you don't want to deal with Sholazar Basin, you could also just stay in Howling Fjord and start farming the Tiger Lily. There are quite a few spawns all up and down the rivers and lakes, I've never had a problem staying busy with that route either in terms of respawn rate. Whichever way you choose, your next goal should be 425. Once you hit that, you can go to Storm Peaks and get the best herbs :)
The south-most section (with K3) can be traveled somewhat safely by a level 70. I'm not gonna lie, feign death or vanish are very helpful. But once you get the pathing of the gnolls down it's not too hard to steer clear of them. If you prefer you can just go directly between the mountain ridge on the NW side and the two zone exits to the south. You can also be a little braver and do full loops of the zone, but you'll probably aggro gnolls here and there. Either way, there's Lichbloom and Icethorn in pretty decent supply here. As long as you're not competing with flyers you should be able to catch respawns as you complete your loop.
I hope this helps those folks who haven't leveled Herbalism yet to find a workable progression path. This is easy to do on a level 70 toon, I did it on the Beta servers and again after Launch. If anyone else has tips to share for Herbing, feel free to post them in the Comments!