Tank skills - offensive

Attack

The most essential combat skill, you won't hit much of anything without it. Train it to 100 as soon as you can.

Axes / Bludgeons / Polearms / Long blades / Short blades / Martial arts / Shield bash

The weapon skill. Improves damage that you do with the associated type of weapon. Every tank guild offers at least one of these. Important to train, but do not focus on more than one of these.

Martial arts is similar, but focuses on unarmed combat instead.

Note

Shield bash improves damage you do when wielding a shield. This is usually done against bigger mobs only, and you do not need to train it early on.

Push, Kick, Bash

Basic offensive skills, faily weak. You will want to train these some early on, but eventually you'll move on to the better ones. Note that some of guild attacks are affected by a variety of skills (for example, Ranger Bladed fury damage is improved by your Kick skill), so you may want to train these some even if not actively using them.

Cleave, Pound, Impale, Slash, Stab

Generic offensive skills, fairly decent. Some guilds only offer these, others have their own ones (such as the afore-mentioned Bladed fury). These are all exactly the same, just with different weapon types (cleave = axes, pound = bludgeons, impale = polearms, slash = long blades, stab = short blades).

For some guilds, you'll want to train the relevant one even if not using them, as the skill affects the main guild attacks.

Reaving, Pulverize, Mangle, Decapitate, Pierce

These skills improve the generic attacks above by adding an automatic second hit to them. Good to have if you are using these skills, not really useful otherwise.

Main guild attack(s)

This is different in each guild, but is one of the most important skills (after Attack and the weapon skill) to train.

Combat damage analysis

Tells you whether the monster you are fighting is resistant to the damage you are doing. Not that important early on, as you can usually tell by watching the mob shape, useful once you get weapons with more damage types.

Enhance criticals

Improves the power of your critical hits. Not essential, but nice to have when you have some experience to spare.

Find weakness

Allows you to score critical hits more often. Again, not essential, but nice to have.

Negate offhand penalty

When fighting with two weapons, the off-hand one gets a penalty. This skill helps you reduce it. As you always want to fight with two weapons, this skill is fairly important.

Stun

Lets you occasionally stun mobs. Not really reliable, and it needs to be trained high (80+) to work well. Nice when you can afford it, not really worth training early on.

Switch weapon

Lets you swap weapons in combat. Useful in some situations, but no need to train this early on, as you likely don't have any weapons to swap to anyway.

Throw weight

Improves damage that you do in melee. Very useful.

Tumbling attack

Counters the Dodge skill, this improving damage that you do. Not essential, but useful to have.