Sima Zhao and Jia Chong go up the left side of the map, while Sima Shi and Wang Yuanji will use the middle of the map. At the beginning, go up the middle path and defeat any officers in your way, as well as clear out the area until you get a report saying that a fire attack is on its way. You will need to be on the southernmost ship (marked on your map) until Ding Feng appears on your ship and sets it on fire.
Defeat him and the ships will be reconnected, so start heading towards the southwest corner as soon as possible. The reason for doing so is because of enemy reinforcements will appear in the southwest. Go and take care of them and then Sima Yi and Zhang Chunhua will appear as allied reinforcements in the south, linking the southern area to the main camp.
Around this time, Bao Sanniang will appear in the south and bring some reinforcements from Nanzhong, which include Meng Huo and Zhurong. Go to the front of the enemy main camp and defeat Yueying to open the gates. Once you do, you might want to clear the area of any other officers before going inside and defeating Jiang Wei to finish the battle.