First. You must have a castle. In either the back, or the center. I find center castles are harder to build, but are generally better looking. Next, a tavern. Shops come next. Then a town square. This should be rural, with a fountain in the middle. Finally, add some Houses. Fill it all with houses. But If you are going to use it for a Server Medieval RP, add a trade hall too. A place where players can advertise their goods and services.