Some extra pointers:
First, I like supporting Sweden's independence on day 1. It is VERY easy to win the war, as you can just block the straight and stop the Danish forces from engaging, and, once freed, Sweden's high-powered army is very handy in beating Poland in the first war (not only the AI now actually use transports, but Novgorod also usually supports Sweden, so they'll have access to you either way). You don't get many easy allies early, and Sweden is a powerful one.
Second, as most people pointed out, you should attack Poland before it gets the PU with Lithuania, and drag this war as long as needed for it to get a king, which will make the PU threat disappear. Also, don't stop hitting Poland over and over until you have ALL Polish culture provinces; it gets accepted pretty early so the provinces are very powerful, and if you don't finish up the job quickly, they WILL get Aristocratic Ideas and this plus their high basetax will make their lands really painful to core.
Third, if you can, get into an alliance with France after you form Prussia; you will inevitably clash with your old pal Austria, and you can end up really lonely then. Of course, if you're a big enough Prussia you can beat everyone at the same time, but you'd rather not do so, and your interests don't really clash with the French for a very, very long time.
Here is my current run, pretty close to forming Germany, and blobbed all over the Baltic. I got two really long regencies AND a Peasants' War, which slowed me down a lot; if not, I'd have formed the reich already. (red stuff on my southeast is Galicia-Volhynia, which I turned into a March for the Marshy March achievement. It got Divine Ideas though, and so makes for a really decent march anyway - all those defensive bonuses stack up heh)
I actually didn't ally France in this run, and it will slow me down even further as I creep closer to Austrian territory. Oh, well
http://i.imgur.com/WQ1Sc2B.jpg