Your first order of business is to capture the two bases that are shown on your map. You also can't go near the two bridges, as your plan will be seen through if you do. Capturing both bases will make Zhou Fang lure out Cao Xiu. In the meantime, you need to break through the southern garrison and go into the southeastern one.
When you get to the above garrison, defeat the officer inside to capture it, then wait until Zhou Fang lures Cao Xiu into your previous main camp. Once he does, he defects back to your side and lights the place on fire. Now, make your way to where they are and defeat Cao Xiu.
Once Cao Xiu is gone, Sima Yi and the rest of Wei's forces will show up in the western and northwestern areas of the map. On the western side, you'll fight Sima Shi and Wang Yi, while the northwestern area contains Sima Zhao and the final officer of the battle, Sima Yi.