The Initial Polish Set up is pretty basic. The strongest possible defense in Warsaw, the 2-3 to the SW of Warsaw and surrounded by 1-3 Infantry units which forces the Germans to make cross river attacks before they can exploit into Warsaw.
Of course they may choose to attack some of the 1-3’s but then the Exploitation attack is cross river which makes it riskier. I have seen a couple of times a German player try that and fail (some really unlucky die rolls) and end up essentially losing the game on the first turn by not taking Poland.
The only real thing of note is that I place the Polish air in Vilna because this forces the German to use his northern air forces to counter air them. It’s not much, but it might make a difference in rare cases.