Herbalism is good to choose if you want an income that keeps up with your expenses without you having to be all too dedicated. As the other professions, this one is just as simple.

Always remember to have your herbalism tracker on and to keep a look at it. It will eventually pop up an herb nearby and it IS okay to grind trough the mobs to get to it. Most people see this as too much work for a single herb, instead you should see it as extra exp.

For the selling part you can follow this simple system to keep AH costs as low as possible:
Put up 2-3 single herbs and 2-3 stacks of 5! yes… by 5 I mean stacks of 5 herbs.

So by setting up small stacks and single herbs you give the alchemist an oppirtunity to get more freedom to buy what herb he wants without having to buy a stack , this results in an increased profit for you.