Your first order of business is to go and rescue Gan Ning, who is in the southwest corner of the map. You'll need to take the winding path to the west to get to Gan Ning. Break through and defeat the officers around Gan Ning to rescue him. Zhou Yu will get injured in the process, which he will use to lure the enemy forces to trap them.
Head north from where Gan Ning was located and go into the garrison there. Clear it of the officers and then wait there until the next wave of officers approach. Defeat every officer that comes to you and once they're gone, the Wu forces will lure out Li Dian, so defeat him when you can. If the main camp is in trouble, which it might be due to Cao Cao's forces entering it, then go and save it.
Lu Su wants you to act as a decoy again, this time attacking from the cliff to approach Xiahou Yuan and Zhang He. Follow the trail given to you and when you execute the pincer attack, defeat both officers mentioned above. Defeating those two will open the door to Cao Ren, who will be the last officer to end the battle.
You need to successfully complete the decoy strategy in order to get both stars on this stage. It's best to play as Zhou Yu for this, as you can control what happens. After rescuing Gan Ning, go north and hold your position inside the base until you lure out Li Dian. It might be best to make an interim save here, in case things get screwed up in the next area.
Once that's done, the second stage of the decoy plan begins. You'll need to follow a specific path on the eastern side of the stage, so enter that area by using the middle path. Go to the north and then around and down the east path. Wait until Lu Su manages to get close enough to Xiahou Yuan and Zhang He before defeating the last officer in the southeast.