I usually play the game as is, but occasionally I use a House Rule for game balance. For instance, in To End All Wars I believe Russia should be required to attack East Prussia to evoke the Hindenburg response.
In ECW players may wish to consider limiting Parliament taking Oxford in the first year of the war. As Oxford is essential to the king's cause with regard to war supply and as the parliamentary player can take Oxford and hold it with little extra effort if this faction makes and early move; the game is a lot more fun and much more balanced to require the Parliament faction to restrain with regard to Oxford.
Incidentally, this is a really nice balanced and fun game.