Thats what i've done to level my herb to max skill in 3 days while doing my other things ( horde only ) : ))

- from 1-75 in the starting areas ( around TB pref )

- 75-150 Barrens

from 150 to 225 i did it in SM , started with GY then at 170 in Cath , you can reset it up to 5 times btw , every run gives you 3 skills up : ))

i went to arathi after 225 , also i found some herbs that don't skill me up but you'll find lots of yellow herbs to pick and level .

at 240 i went to hiterlands , i made Jintha'Alor run  ( I'm 70 ) and made some runs around to 265 then i went to ferales to 300 .

from 300 to 375 is easy i guess , pick some in hellfire and zang is your place to rock : ))