I usually go for pomerania and prussia first, after then takuing both Volhynia and Lithuania you have your first secure province - prussia. Too bad you still have 4 borders then (5 if you've taken moldavia too (and you should)).

After that sweden and Livonia beckons but it becomes more a matter of reacting. Is HRE falling apart? then invade. Are the Novgorods bungling around? put them out of their misery. Hungary and Poland can coexist for quite a time in peace in my experience.

You get the picture.