The best way to equip dwarves is to assign them a uniform.
The optimum arrangement is;
metal mail shirt
metal mail shirt
metal mail shirt
metal breastplate
leather cloak
leather cloak
leather cloak
leather cloak
leather cloak
leather cloak
leather trousers
leather trousers
metal greaves
metal gauntlets
leather mittens
socks
metal high boots
metal cap
metal cap
metal helm
leather hood
leather hood
leather hood
leather hood
leather hood
leather hood
metal shield
weapon (ranged or melee)
and they will also pick up waterskins, backpacks, and quivers as they need them.
Remember to set on the uniform screen to replace clothing, set exact matches, and on the military screen (I think it's in the schedule section) to set it so that dwarves are uniformed off duty. However, if you put it to these settings, dwarves will immediately cast off their clothes to conform to the rules. If they can't find the armour assigned to them, they will wander about naked (at least partially). Also bear in mind that if you continue making new armour and weapons, military dwarves will spend all their time picking up equipment. As far as I can tell dwarves won't obey any orders until they are equipped, so my guess is that the correct armour isn't there for them to wear. However, if dwarves are casting off their civilian duds, that may cause danger room problems because even clothes provide suitable protection against noquality training spears; so, in this instance, you could set the uniform to partial match over clothing, so that dwarves won't cast off their civvies immediately. However if you do this I don't think they'll put them on, just not take them off in the first place. I don't know, I don't pay much attention to clothes.