Culture, by definition, is the sum of rituals and value systems created by a community of people. So any group of people who spend lots of time with each other will eventually develop their own culture, even if it's unconsciously. You can have a culture within a group as small as a family! By that definition one small town would have a different culture (which manifests as ambience, atmosphere, attitude) to another small town down the road.

If you want to build a culture from the ground up, the first question to consider is: what are the values shared within this community? What objects, things, or traits, are important, valuable, to be honoured and upheld? From your values come rituals, which are behaviours that dictate what is good and proper.

More questions: What is the geography/environment like? (Because environment does play a role in culture building, eg. a coastal community would value the ocean more than an inland community.) What kinds of rituals surround those values, why were they established, what is the meaning? (Not just religious rituals, but civic ceremonies like marriage, coming-of-age, etc, as well as private behaviours, such as within a family or a romantic couple.) What kind of cultural expressions (music, arts, theatre, fashions, etc) do they value and enact? What consitutes civic responsibility, what makes a "good citizen", and why? What is the governance/leadership like, and why?

Also, culture does not develop in a vacuum. Your town will have transaction with the outside world, and have continual transactions through time. There will be constant tension and dynamism between the established, normative culture, and constant new influences from without. So what kind of external cultural influences are being brought in, and will they be embraced or rejected?