Mount Hyjal is probably the worst zone in the Cataclysm expansion for farming Herbs, though, depending on prices at the Auction House and the number of farmers on your realm, you may find that the lack of a "unique" herb in this zone makes it so that the common ones aren't farmed nearly as frequently.
More nodes per hour means more Volatile Lifes and even if the price per stack isn't what you want on the Cinderbloom and Stormvine found in the zone, the quantity will make up for it. Basically, Cinderbloom grows anywhere east of the black line on the map in the blighted areas of the zone. Anywhere that there is fire is especially fruitful for Cinderbloom. Conversely, Stormvine grows in the lush grassy areas of the zone to the west and north of the black line. There is no true herbing route in Mt. Hyjal as the herbs seem to be dispersed. Like always, look for flat land and avoid the hills when looking for herbs.
If you can't find an herbalism path that suits you in Hyjal, you could pick up mining as a secondary profession. If you stick to the blighted area of the zone, you could farm a lot of Obsidium ore and Cinderbloom in a quick amount of time. Simply following the blue line on the map will cover many of the Cinderbloom nodes along with the Obsidium nodes.
Keeping an eye on the Auction House market will enable you to put your WoW gold-making efforts to where they are best suited. While Mount Hyjal doesn't offer the same opportunities that other zones do in the Cataclysm expansion, each realm is different. Trying out various areas and seeing which works best on a gold-per-hour basis is usually better than insisting that one place is the perfect spot. It usually isn't, and if it is, there's a good chance that many people know about it and will turn it into an over-farmed frustration before you can blink.
Mount Hyjal Mining Route
Vashj'ir Mining Route
Deepholm Mining Route
Uldum Mining Route
Twilight Highlands Mining Route
Mount Hyjal Herbalism Route
Vashj'ir Azshara's Veil and Stormvine Route
Deepholm Heartblossom Route
Uldum Whiptail Route
Twilight Highlands Twilight Jasmine Route
Tol Barad Azshara's Veil and Whiptail Herbalism Route