Here's a sneaky thing: two fighters, both with shield and weapon, let's call them 1 and 2. 1 attacks, while 2 does Aid Another to add +2 to 1's AC. The next turn, 1 gives Aid Another for 2's AC, while 2 attacks. Repeat the process. Especially annoying if both have Tower Shields, to give themselves cover when not attacking.
Three warriors standing abreast. One has a reach weapon, while two have medium melee weapons. When someone approaches, the one with the reach attacks, and when they step within fighting range of all three, the one with reach takes a 5' step back, while the other two Flank.
*sniff* Kyramus, beautiful.
Remember, kobolds set traps. Traps in their tunnels, traps around ambushes, traps to keep Meleers and their ranged men seperate.
Ditto for what Kyramus said, about short tunnels, traps within the tunnels, and ranged attackers. Kobolds have darkvision, so they could install oil traps hidden in the ceilings of their tunnels, made to go off when the heat of a torch passes under them.
Humanoids who keep pets, or use things like a wasp nest. Throw that in the middle of camp.
Murder holes in the ceiling of a dungeon is good. Any creature with a spear or ranged weapon, or bubbling oil/acid just pouring down through the murder holes ontop of people