I vary, but if I'm dealing with more than one culture/country, I start with deciding what I want to base those cultures' names on. So when I rewrote Shattered Ivory from fanfic to original, I gave one country Welsh and Welsh-inspired names and the other Anglo-Saxon/Old English names.
Then I decide which time period I want to 'reflect' and which cultures. Doesn't stay strictly the same. Both my big fantasy worlds have forms of running water, based on the idea that if the Romans could do it, so can they. The discovery that combs were an important sign of civilisation amongst the Celts resulted in my use of an offering of decorative hair-combs by a man to a woman being tantamount to a promise of marriage.
Culture is naturally associated with climate. If it's northern/temperate, fabrics will be wool, fur, leather and probably linen. Silk, cotton and similar fabrics would be gained by trade with warmer climates (unless you invent a new kind of silk). In many climates, horses are of vital importance as the strongest animal for bearing human weight and thus dramatically speeding up travel time.
I find myself doing all sorts of little bits of world-building completely unrelated to what I'm researching all the time. Let it flow - you can always change it later. Just keep things consistent.
Avoid building too much - you can end up stifling the story itself if you try to make too much of it. The world needs to serve the story, not vice versa.