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In the areas of practice in which various Jewish communities differ -- such as whether fish counts as meat (it does for Sephardim, not for Ashkenazim, for instance) -- one typically follows the practices of one's father, if father and mother are of different backgrounds and customs. If one's father isn't Jewish, or converted and has not yet chosen which minhag (custom) to follow, then one follows the practices of one's mother.

You go by the mother's FAMILY tradition. If the family have essentially been non-religious for as long as anyone can remember, you go by her ethnic heritage. So, if your mother and her entire non-religious family (up the patrilineal line if possible; if not, by her matrilineal line) are Hungarian, say, you'd go by Ashkenazi customs and practices. If she's Portuguese, go by Sephardi customs and practices.

Special note, because I'm Dutch myself, along my mother's lineage: Dutch Jews are mostly Sephardim, not Ashkenazim. That's because most Dutch Jews came to the Netherlands from Portugal. If you're of Dutch heritage, and not sure whether the "ancestors of your ancestors" were Portuguese or from Germany/Denmark, go with Sephardi, because it's more likely to be correct. Either that, or look at the features of your family and make an educated guess: light skin, blonde or light brown hair, blue or green eyes = Ashkenazi; darker skin, darker brown hair, brown or green eyes = Sephardi. But that's a vast overgeneralization, so don't take it as Torah mi-Sinai.

I'd think so.

To Divash: Thanks for the help. I guess I'm Ashkenazi, now.