This is one of the first battles for most characters, and is fairly easy. You start off on either the southeast or southwest corner of the map; when the battle begins, move forward and take over the base in front of you. Now circle around to the center camp, defeat the officer here, and lower the drawbridge.
Your forces will cross the bridge, but watch out for the two officers who will attack you from behind. Take over the base at the bottom of the stairs, and go right. Take over the bases and gates you come across until you reach Zhang Man Cheng. He is tougher to take out than the other officers you have come across, and to make things a bit harder, he activates a series of fire-breathing statues. Defeat him, take out the other officers that rush in, and look for a large cauldron with green flames. Destroy it, and you'll be halfway done with Target 2.
Go around the Yellow Turban Main Camp, and move toward Zhang Liang. He'll conjure Phantom Soldiers, and they'll explode if you attack them, so just run past. Zhang Liang is as tough as Zhang Man Cheng, and the phantom soldiers do make things harder, so be careful. Defeat him, and destroy the cauldron to complete Target 2.
By now, the only real threat left is Zhang Jiao, and everyone in your army should be attacking him. Help them out, and soon you'll bring him down, and if Huangfu Song and Zhu Jun weren't defeated, Target 3 will be achieved!