House Stark, despite being the house with the most unthreatening access to nearby land, should be relatively easy to play away from the hectic land grab going on down south. However I really don't understand the strategy for House Stark, at least with the southern factions it's fairly easy to know where to start with expansion and working with the other players but with Stark I don't know where to begin after taking the initial few territories. The big difference with Stark, particularly with my group, is that it's midgame moves remain relatively unchecked as long as it's not making a direct attack on someone. With so much going on in the south then with my group then Stark often has the option of wandering the regions around the Eyrie with only minimal complaint from Baratheon, though sometimes an Eastern expanding Greyjoy can end up cutting off Stark's southward bound moves.
I'm just not sure what to be doing when I play House Stark.
What should a good House Stark player be looking to do? What are it's main threats? What counters can other players employ against House Stark? If Stark gets close to winning then realistically it might only be Baratheon and Greyjoy that can do anything about it with maybe a bit of Lannister help. If another player is getting close to winning I often feel far away from being able to help stop them.
As an idea of my groups play set up then we generally use the ACoK expansion variants: ports, OTOs and the ACoK house cards.