Most dwarven societies expect military service from every capable member of the community; so Dwarven PC's likely served in the military a standard of ten years before their adventuring days.
Dwarves, whenever possible, fight in small specialized teams consisting of 2-4 soldiers rather than in massed armies. They are way of enemy spellcasters and massed missile volleys. If terrain is favorable to larger units, they might do squads of eleven to twenty with few commanders mixed among them. This is still smaller than most enemy formations and often break down into smaller teams as necessary. They often fight in mixed bands of Fighters, Clerics, Wizards & Rogues depending on specific missions.
Dwarves prefer to fight at night when their darkvision gives an edge against the enemy. They choose battlefields to counter opponents' advantages such as speed or mobility since Dwarves are slower. They position themselves so difficult terrain separates them from enemies. They then challenge enemies to attack while preparing to fight on the defensive, littering the ground with traps like pit traps, sharpened stakes, caltrops, camoflauged trenches and pools of flammable oil.
When the enemy charges, dwarven crossbowmen and archers wreak havoc with volleys of bolts and arrows. by the time enemies enter melee, they find themselves wounded, disorganized and demoralized. They favor destroying the strongest enemies first.