Hi it's my first post... :)

I've played a lot with this nation. Well i'm Polish :)

There was many posts about Polish units, i would just like to add some things.

Retainers is a dump unit, you get Polish Knights just after and they soon replace them, and Hussars are far more better flankers.
Polish Guard is a tank. Just let them hit whatever is in your way (except pikes :P). The difference between them and PK is simple, they have more stamina, they don't charge without orders and they have a horse in plate armour which adds a lot to charge and missile defence.
The missile units are superb, have notthing to add, well maybe that Lithuanian cavalry comes to late to be usefull. Strzelcy are far more better.

Missile units do suck. Only one good and just for the stakes. U have to use missile cav for the ranged assignments. Well until you have gunpowder. Arqebusiers are sometimes usefull.

As for the foot soldiers. You have some to choose from. But the best DPK are your weapon of choice. HRE has nothing on foot that can counter them, just like Hungary. You could have trouble with the Russian and Danish AP infantry if you are forced to fight them 1:1. Spearmen are your basic infantry, nothing special but they do their job well. Now woodsmen... an AP attack and cheaper then peasants. A perfect auto resolve unit. Use against the hordes if you are on the loosing side.

As for my strategy. As said before you have to be quick. Take breslau just when you get the quest for it. you will be awarded 4x Polish Nobles. Take the units form Cracov to breslau and then with joined Noblews take Prague. After Prague i go north for Magdeburg. With the north force i take Thorn and make it a city. Leave one unit there and the rest runs fast for Stettin, makes a siege and is supproted by the Magdeburg forces. After the battle i make Stettin a city.
In the east i produce 2x PN and 2x Strzelcy. Take the whole army south and occupy Iasi which i turn to a city. If the Hung's or Byze's don't rush it i take Bucarest.
Then i turn East to take Kiev, Wilno, Ryga and eventually Novogrod. I make Kiev a castle despite it's economicall potential. It will be my main defence against the hordes.

I leve the east and concentrate on the west. Where the HRE will start by now to alk around my lands with soldiers meaning they are up to something.
Sacking and pillaging Frankfurt and Norymberg and then giving them to the Pope secures your west border.
Now you have 2 options, well maybe 3. You blitz the danes and secure the Baltic sea or you could go south.
Usually i bleed out the danes in 3-4 turns and then i go south. Hungarians keep the alliance long enough and fight with Byzantines and Venice so they are an easy target.
Once you get Constantinopole it's all straight forward.
Personally i like to invade Britain cos expanding the west border is not much fun for me. Besides i have the Pope there.