As you approach the open area ahead, ballistae on the cliff to the east will begin firing, as well as archers to the west. You will need to defeat all of the officers in the area in order to make Wei retreat, which will grant you access to the east and west sides near paths that lead to the main camp. If you're playing as Jiang Wei or Ma Dai, then use the ladders to the west; if you're either of the other two officers, go through the eastern garrison.
Go through whichever side you're on until you break through the defenses, which will trigger some trash-talking. This will cause Guo Huai and Zhuge Dan to come forth and challenge your own officers, so defeat the one on your side and the other should fall as well. Zhuge Liang has a plan to fake his own death and temporarily withdraws from the battlefield, with Shu forces retreating to their main camp.
This makes Sima Yi actually think Zhuge Liang has died and he sends officers in pursuit. Make sure that Wu Ban isn't defeated at this time, as he is the commander of your forces. Defeat the pursuing officers and Sima Yi will send out messengers for reinforcements to the east and west, so if you can intercept them, it will mean less officers you might have to take out.
At this time, Sima Shi and Sima Zhao will both open the main gates and make their way towards the Shu main camp. This will turn the central area into a nice big gathering of enemy officers, so make sure you go around and get them all. Eventually, Xiahou Ba will spawn to the east where the reinforcements came from, so stick around if you are finished to take him down. All that's left is to make your way to Sima Yi and finish him off to complete the battle.
This is one of the harder stars to get, simply because there are two objectives on opposite sides of the map. At one point in the battle, messengers will appear that go to specific points to call in reinforcements. There are only two, but you need to defeat both of them to get this star. It might be easier to use Wei Yan for this one. You will likely need three Musou bars for this, so come back if you don't have them yet.
Begin the battle like normal and follow the orders given. When Wei Yan calls Sima Yi a coward, Zhuge Liang will make you retreat, but don't listen to this mission. Instead, Sima Yi will send troops after you, so stick around and defeat them all. Once you do, the messengers will appear for the reinforcements. Defeat the one in the northeast corner, then use the Musou with the horse to reach the other messenger faster. If you get both, then the cutscene at the end of the battle will be slightly longer.