The primary reason for harvesting is to find the raw materials you'll need for crafting.  Adventurers too can head out into the wilds and harvest materials for which to sell on the broker or they can get an Artisan to craft them some nice gear or house items.  As for the Artisan, harvesting materials is a must and buying them off the broker can get really expensive at times.

As you wander throughout the lands and dungeons of Norrath, you will come across "nodes" represented as logs, dens, fish, rocks, roots and bushes.  As you move your mouse over these nodes, they'll begin to glow and change the icon from a pointer to a hand which indicates it is of interest.  If you right click on the node and examine it, you will find information regarding the minimum harvesting skill needed for that node in order to harvest rares from it.  Double click on the node to quickly begin harvesting it but I find the following steps added into a macro far easier; and you can harvest while flying using this method.  Then just place this macro somewhere on your hotbars for easy access.

Each node will allow you to successfully harvest (pull) from it three times.  Finding a node with less than that usually indicates it was not fully harvested by someone else.  If you fail to harvest anything from the node, just keep trying until you succeed.  After a node has been harvested successfully three times, it will vanish and in a while it will respawn; either as itself or as a different node type and possible in a slightly different location.  Here are the six possible results you can expect to achieve; note that fish nodes do not contain imbuing or rare materials and if your havesting skill is below the tier's minimum requirement that you will not be able to achieve the last two results in this list.

There is a chance to recieve a free double (second) harvest when you succeed at a harvesting attempt.  The chances of this are based on the tradeskill specs you've allocated, the gear your wearing and from a bountiful harvesting potion.  The maximum double bonus chance is currently 55%. If you do get a double harvest, the game will randomly select one of the above six results appropriate to the node type you're harvesting.  So on a single harvesting attempt, at best you could receive is two rares and twenty common materals.

So I've mentioned a harvesting skill.  This determines what level (tier) of nodes you can harvest and your chance of success when harvesting.  You can view your current skill level for each node type by opening up your Character window, then skills tab at the side, and then the general tab at the bottom.  There you'll see your current skill level for the six node types.  Each attempt at harvesting a node has a chance to raise your harvesting skill for that node type for that tier.  Each harvesting tier has a level cap associated with it and your harvesting skill for a node will not progress beyond this unless you adventure to the next tier of harvestable nodes.  So depending on which nodes you harvest often, it is possible to have a different harvesting skill level for each of the six node types.

For each tier there is a base harvesting table and a bonus harvesting table and your unmodified harvesting skill will determine which of the two you will use.  The bonus table just gives you a higher chance of receiving a greater number of common materials and a higher chance of harvesting a rare.  Both tables are dependent on the type of node you're harvesting; for example, since stone nodes contain two types of rares, the chance of getting a rare is slightly higher for this node type.  The base harvesting table is the default.  The bonus table on the other hand has a random chance of being used if your unmodified harvesting skill is at or near that tier's harvesting cap; for tier 10 the cap currently cannot be reached with an unmodified harvesting skill (maybe around a 510 skill level).

You can increase your chances of getting a rare buy using various gear and potions along with applying some AA points into specific tradeskill specs.  The best you can do for now is a 14% increase in rare chance along with a 80% increase in the double harvest bonus.  Which means there is an extremely small chance that you could actually now get six rares by harvesting a single node.

For tier 1 nodes, there is a far higher chance of getting rares than all other tiers.  This can be beneficial if you're looking for a very cheap way to level up your transmuting skills.  Just harvest the ore, stone and root nodes and craft the rares into spells and master-crafted gear.  Then transmute these but be warned it can slow down as you're transmuting skill levels higher.  The benefit here is that the cost will be only a few copper pieces for each attempt.

The two methods for harvesting an area are either by "Cherry Picking" or "Clear Cutting".  The Cherry Picking method is where you will harvest a specific node type.  This method is fine when you need a specific material type.  The problem here is that in older tier 1-5 zones a node will respawn as a different type and in a different location and over time you will find a decreasing number of the nodes you need.  For tier 6 and up, a node type will always respawn based on its location: ore and stone nodes spawn near cliffs, rock outcroppings, mountains and caves while roots, timber and shrubs will spawn in locations of forests and grasslands.  The Clear Cutting method is simply just harvesting every node you run across and offers a way to gather a wide variety of resource materials.

I've included a resource web page listing the common materials harvested from nodes and their zone locations.  This page also indicates the starting level necessary to harvest that tier along with the level cap associated that that tier.  Since the starter zone "Isle of Refuge" is obsolete and no longer accessible, I've excluded it from the zone locations.  Any special materials, such as for seasonal holiday crafting, is shown on the special mats page.  I've also included a page listing obsolete crafting materials that can still be substituted into existing recipes.

If your going to head out to harvest materials, you better then equip yourself appropriately.  The following items in this section list what can be done to reduce your harvesting time per attempt from 3 seconds to 1.5 seconds, rare chance up to +8.0% along with increasing your double harvest percentage chance upto 67%.

Tailor made Harvesting Gear:  This items will decrease the harvesting time and increase the double harvest chance for each harvest attempt.  This recipe is found in the Tailor Essential Vol 90.

Woodworker made Harvesting Tools:  These items will decrease the harvesting time and increase the double harvest chance for each harvest attempt.  Each tool requires a minimum adventurer or artisan level to use and the higher the level the better the quality of the tool.

Tinkerer made Harvesting Tools:  These tools are available to both adventurers and artisans and they decrease the harvesting time as well as increase the harvesting skill as related to a particular node type.

Far Seas Traders Harvesting Tools:  You'll not only need to meet the level requirements for these items but you will also need to meet the minimum faction requirement for the Far Seas Supply Division in order to purchase them.  Also, you will also need a certain amount of Far Seas Trading Company tokens and some coinage when you purchase them.  Duration for all these tinkered items is 10 days.

Quested Gear:  The following is a list of gear related to harvesting that can be quested for.  Listed is the gear and the havesting stats that are enhanced when the gear is equiped.  Click on the link to view any other related stats.

Collection Items: 

Tradeskill AA and Prestige Abilities:  By applying AA or prestige points initially into these skills will allow you to use them.  The more (up to 5 points) you apply to them, the better the ability becomes.

Harvesting Potions:  The Elixir of Mara is a potion you'll receive in the mail from Lian Augren when you harvest your first node and is a prelude to the Gathering Obsession quest line.  It's meant to intice, I mean introduce, you to visit Qho.  The Harvester's Balm can be crafted by those that have completed the third quest in the Shipwrecked Timeline.  The Bountiful potion is recieved as one of a possible six potions from your tradeskill apprentice.

Racial Bonuses:  The following races get an inherited bonus when it comes to harvesting.  This ability can stack with other harvesting time reductions.

Beta Rewards:  The following are tradeskill rewards you can achieve by completing a series of quests and/or events when playing on the beta server for a given pre-expansion release.