The gods of the North are nameless and numerous (I: 6. SSM: 1)
The First Men and their descendants in the north largely follow the old gods, which were worshipped by the Children of the Forest (I: 19, etc.)
Every castle has its godswood, at which the center is always a heart tree with its face (I: 19)
The places where carven weirwoods stand are sacred, and are not defiled by bringing animals such as horses into them (I: 435)
In the North, only a few houses do not worship the Old Gods, following the Seven instead (I: 476)
Beyond the Wall, the old gods are the only gods (I: 482)
The Blackwoods follow the old gods, and are one of the few southron houses to continue to do so (I: 661. SSM: 1)
Some men believe that it is impossible for a man to lie before a weirwood, because the gods will hear (II: 150)
Incest is a monstrous sin before the gods, but the Targaryens followed the practices of ancient Valyria and didn't answer to religions when it came to such issues (II: 364)
Even in the North, septons witness marriages (although this may not be the case if both parties follow only the old gods) (II: 384)
Marriages are also made before the heart trees (II: 384)
Old gods or new, it makes no matter, no man is so accursed as the kinslayer. However, there are degrees of kinslaying, and killing a distant cousin in the midst of a battle is much less of a problem than killing a brother in cold blood (III: 232. SSM: 1)
The old gods hold slavery as an abomination (III: 264)
The old gods are said to still linger at High Heart, keeping a red priest from looking into his flames and seeing visions (III: 492)
Among the wildlings, it's believed that when one dies, the old gods take the person down into the earth and into the trees, to be among them as they inhabit all things (V: 13)