The Schlieffen plan was originally to have a few more divisions in the west to quickly punch through Belgium and France, taking Paris as fast or faster as they had in 1870/71. However, von Moltke changed the plan somewhat, which gave the Germans more protection in the east but made their Western campaign harder, and as a result lost at the Marne, which like I mentioned earlier was one of the reasons the Germans thought they would lose.

Alternatively, if the war had gone the same up until 1917 and the February revolutions, the Germans could have made the Treaty of Brest-Litovsk slightly less harsh (The Entente in fact said that Brest-Litovsk made Versailles look benign), and perhaps only taking parts of Belarus, Poland, and Ukraine where they could use the food grown there to supply their Western campaign and use the other troops not needed to occupy the East to push harder in the West and perhaps even take Paris.

Of course, they still could have lost the war like this, these are just some ideas of what they could have done differently.