Do you have any tips?
Hanover to Wrocław - through Leipzig, Dresden, onwards.
Wroclaw to Poznan - S5 from Wrocław to Leszno, then onwards to Srem (DW433? I think? I don't remember the number...) and pick up the S11 in Kornik into Poznań. Avoid taking the DK5 between Leszno-Poznań.
Poznan-Prague - Go from Poznan to Frankfurt (Oder) on the A2, then B87 through Beeskow to the A13 towards Dresden. A17 towards the Czech Republic, then D8 from the border to Prague.
Don't take the routes for Poznan-Prague that Google recommends, they suck.