I can't tell you what would drive in the folks by the millions, but I can tell you some of the things I like:
Authenticity: teas that reflect tastes and criteria developed where people have drunk tea for centuries and grow it: China, Taiwan, India, Japan and good traditional blends for export.
Tasting: I don't buy tea I haven't already been able to try, for the most part, unless something comes highly recommended by someone I know. (I freely acknowledge this is because I'm lucky and spoiled to be able to do this.)
I often taste and compare teas, for example teas in the same category. So there should be a tasting option priced for say, three teas at once or more if that's what someone wants. Let's say there are five new teas from a season of Taiwan oolong: it's a nice introduction to be able to taste and compare the variety of flavors.
There's nothing like a tearoom that reflects the traditional idea of being able to spend time and relaxing: talking to friends or reading a book, etc. That doesn't mean you want people to park for hours with computers (although many traditionally minded tea houses allow it because it reflects the traditional idea of a teahouse as a place to do everything, including art and business), but it does imply a particular atmosphere.
Sell tea snacks or very light foods - it will make some money, hopefully, and people will be able to keep drinking tea.
Tea Ware and teapots for sale, and books esp on tea. Lectures and tastings are great. Have copies of "Teahouse," the play by Lao She
And good, polite customer service a must; great bonus having people who can answer questions and enjoy talking about tea and sharing their knowledge - who love tea. I think snobbery for its own sake is idiotic, there's always someone who knows more than you do: people should be able to be polite to those who are brand new to tea.
That's where I'd start.