They are a vassel of Poland, so only the GH will do much of anything and you can make peace with them although their provinces are tempting to grab, don't bother trying since the GH will destroy you easily. Just concentrate on diplomacy and increasing your manpower, marry away your family to the likes of hungary, poland etc. and try and begin to align yourself with Austria and Bohemia so you have a good ally once you split from Poland. After that get on a boat take out an african tribe wait till it cores and then go grab some colonies in the Americas. You are also surrounded by small neighbours, so if the opportunity arises take them out do so. Wallachia, Bosnia, Transylvania will be easy meat at times and the Ottomans are usually weak enough by the 16th century to take some provinces from them although in my experience it's more trouble than it's worth. To be honest, I find Lithuania more troublesome.
