Look up old maps! It's generally not going to be relevant to have a fantasy town with the wholeass medieval feud structure, but it's good to find things you might've overlooked.
Think about geography! The town will have a certain orientation and paths depending on what's most important for people to get to first. Elevation is also important, you don't want to have a very flat-looking place unless it's on plains (something I almost did on Centrasight for my comic).
3D models are very useful! Save yourself some time during this extremely painful and long process of trying to match everything to perspective, even some very simple house-like shapes will do to speed it up.
And something that's really important, if your story isn't specifically european, don't stick to just european inspirations. Tons of cultures had very nice looking towns at the same time period, or even cultures from before that time! Wealth, location, resources that they can get or give, that all can change your fantasy town into something very particular.
I was real smart and forgot to name this picture with the source, but I believe it's the painting of an Aztec or Mayan city. It's a very flat area, but there's already a huge difference with the vegetation, very large public areas and "flat" looking buildings.