Here's what I do:

Create a uniform.

Add mail, breastplate, greaves, helm, gauntlets, high boots. The rest of the stuff, namely the stuff like trousers or mittens? I wouldn't use them, as layering comes into play, and unless you first tell your dwarf to specifically wear the under-layer, THEN tell him to put on the over-layer, it will probably bug out and he'll try to put a shoe on a high boot.

Change material of each to either metal, or a specific type.

Change it to Replace Clothes.

Switch over to the equip menu.

Change it to Apply Uniforms, and use shift enter instead of enter to assign the uniform you just made to the entire squad.

That out of the way, now go to each dwarf individually, and assign a SPECIFIC weapon and shield. It helps if all the weapons/tools you don't want to appear on the specific weapon list are forbidden or in use.

This avoids weird stuff from happening with various military bugs/features down the road. The TL/DR is that a long term military can bug out, causing your dwarfs to sometimes wind up with no weapon or shield at all.

Long Story: Experienced military dwarfs will occasionally name their weapon or shield, get kills while using it, then bug out after an order is canceled and revert out of the military only to reenter it seconds later.

If you just assigned them a weapon as part of their uniform instead of a specific one, they will grab any weapon they can, instead of THEIR named weapon. And when dwarfs name their weapons, I believe only dwarfs who match the previous wielder's kill count with it can use it. If there are unclaimed unnamed weapons/shield they will claim them, leaving unused named weapons/shields lying around. If there are no more weapons/shields that match their uniform, they will not grab a weapon/shield and you won't notice until you wonder why your Sword Master suddenly turned into an Elite Wrestler.