Who is the sponsor for the course? A town Rec Department? A local school? Regardless of who you are working with, you have to expect that not everyone is going to be an avid disc golfer and know every last detail about the sport, conventions, and considerations. Therefore, its helpful to outline and discuss even the small details that would make course development a success[1].
Site Planning

It almost goes without saying that one of the first things you have to do is identify where the course is going to be built. It may seem obvious ("we're going to build it right here"), until you get into the details of construction and layout, conservation approval and more. Your town or state probably has a GIS system that will show property / tax boundaries that help in defining the abutter's property.
Software
Given a "canvas" on which to draw a course layout, the actual process of depicting teepads, paths, baskets, OB, etc. can sometimes be done in creative ways. The example here was done with Inkarnate - online software for mapping fantasy worlds.
QGIS (formerly Quantum GIS - see wp:QGIS) is a spatial visualization and decision-making tool that is completely free software.

- ↑ Here is some advice during the development of the Weare-Merriman course in Seabrook, NH