If i was Adolf Hitler and i had decided that i was going to invade Poland, i would expect at least that Britain and France would envoke their mutual assistance treaties they had with Poland, thus effecting them to declarations of war, now having said that i would have had to.

1, Order plans for the eventual invasion of the west, this was done historically.
2, Order plans for the eventual invasion of Britain, should have begun by June or July 1939, to build up supply invasion vessels, to train and implement the fine art of amphibious landing, order the Luftwaffe to practice torpedo attacks and the like.
3, Never have allowed the escape of the BEF and the French at Dunkerque.
4, Under no circumstances entertain an Armistice but a full Unconditional Surrender to France and seizure of all French Naval units in Home and North African ports.
5, Here is the tricky bit, a full invasion of Britain, knock her out of the war.
6, Insist that as per Surrender Treaties, defeated nations such as France and Britain under Pro-Axis puppet governments sign mutual assistance treaties.
7, Convene a meeting with Axis partners to clearly define a "Soviet Union First Policy".
8, Agree to keep the U.S out of the war at all costs.

I can add more stuff but my time is running short.