Determine the map's purpose. If you're making a map of local nature trails or a map of the bus and train routes in your town, then that is the map's purpose and why it will be used. It should explain something to the person reading it, and ideally it should be as simple to follow as possible.
Consider your audience. If this map is going to be read by professional survivalists then it's going to look a lot different than one intended for children. This perspective should be kept in mind throughout the project, especially when you're designing the symbols and legend.
Decide on the details. Choose the symbols that you're going to use, as well as the scale that you're using to represent the distances the map displays. Choose whether you're going to use a reference map or a thematic map for your purpose. Design your map's legend and give it a name. Also put the compass on the map so people know which way is north.
Draw out the map. Use everything that you decided on previously to create an accurate, easily readable rendering of the area you're mapping that draws attention to the special purpose of the map. Don't be afraid to use contrasting colors to mark out important areas. For instance, roads are color coded in atlases because it makes them easy to find against a blander background. Tricks that draw the eye can greatly enhance your special purpose map.