Master of Arms

	Master of Arms	10
	Raise four weapon skills to 400.
Criteria: Requires 4 out of the following 15: Template:Col-2 Axes(400) Crossbows(400) Guns(400) Polearms(400) Swords(400) Two-Handed Axes(400) Two-Handed Swords(400) Wands(400) Template:Col-2 Bows(400) Daggers(400) Maces(400) Staves(400) Thrown(400) Two-Handed Maces(400) Unarmed(400)

Master of Arms is a general achivement.

Every class starts with at least three weapon proficiencies, and they can purchase training from Weapon Masters for two more. All classes start with training for Unarmed combat.

Strategy

You can skill up unarmed to 400 to complete Did Somebody Order a Knuckle Sandwich? and it will count as one of the four weapon skills you need to complete this achivement.
It's best to equip weapons that have very low DPS and fast speeds, because your chance of skilling up is per attack, not per kill. White items you can purchase from vendors in the starting areas, or grey vendor trash items are good options.
You can skill up on mobs far below your own level, to prevent the damage that you would take, but you will get fewer hits on them before they fall down.
The Grove Walkers directly underneath Dalaran can last a long time if you have a weak weapon since they regenerate themselves, if you can take the damage for a long time. Something like Seal of Light or Blood Presence would make this very easy.
Characters with combat pets (hunters and warlocks, plus other classes depending on spec) can use their pet's taunt abilities to keep the mob's aggro, reducing the damage the character takes, while keeping the pet in passive mode to keep the mob alive longer.

You cannot skill up by attacking mobs that are immune to damage; for example the Traning Dummies found in capitial cities are not good for practicing your fencing abilities nor sniper skills.