Herblore is a member's skill, so if you're not a member or will ever become one, then don't read this guide. This guide requires huge amounts of herbs and vials, so you can either kill chaos druids and stockpile the unidentified herbs in your bank or buy them for 1k each and buy vials from players or from shops.
Before You Begin:
You must finish the Druidic Ritual quest before starting the herblore skill. You will also get 250 herblore experience as well.
Level 3-12:
Get 50 Guam leaves, eyes of newt, and vials of water. Use the herbs with the vials of water, then add the eye of newt to make them into attack potions. If you don't need attack potions, then you can make antipoisons with marrentill after getting to level 5.
Level 12-30:
Get 215 Tarromins, limpwurt roots, and vials of water. Make strength potions, and if you need money, you can sell them. At level 19, you can make guam sludge for the hunting skill, so you can switch to that.
Level 30+:
Make whatever you want, since most potions past this level are useful and good to sell.