If your goal is a "simple" coffee shop, I would say it's important to locate it somewhere that's guaranteed a fair degree of foot traffic, such as your city's financial district. Check mobile applications such as Yelp or Foursquare to see where other coffee shops are located, and what their reviews/ratings are - although you may not want to move in right next door to an existing, established shop, you may find it beneficial to locate your shop just down (or across) the street. This way you can ensure the foot traffic initially drawn to or near the other shops see your coffee shop and check it out.
Alternatively, it helps having two coffee shops across the street from each other to get foot traffic both ways (one example being Coffee Bar and Workshop Cafe, which are immediately across from each other on Montgomery Street in San Francisco).