It's very simple, poland has the best cavalry gens in the game so, just follow this and you will surely win.
Operation Steel Kielbasa
Task 1.
Move dabrowski and other cav general into north prussia.
Task 2.
Move your forces into vilnius from the north east.
Task 3.
Move your eastern forces to russia but do not engage, wait for them to engage.
(Note: Do not attack austria as they will not attack you, but if they do defend them or just restart.)
Operation Expand
Task 1.
Attack prussian forts and danzig
Task 2.
Take Vilnius
Task 3.
Conquest into the baltics.
(Note: Wait for the general from russia in the south to attack, he hasn't yet)
Operation Sauerkraut Sammich
Task 1.
Engage into the west heavily, if the prussians or austrians have taken poznan, retake it and move on.
Task 2.
Fight for berlin
Task 3.
Keep fighting to riga in baltics.
(Note: The russian general I've been talking about for the last few operations, remember him? Yeah, he's assaulting your fort.)
~This has been my first part to Dummies Guide Poland 1809, if you want me to continue like or reply to this.
(Further Note: This is for Newbies not experienced players also, this is supposed to be comedic not very serious)
There are much better beginner conquests.