Found some rules to cartography online from http://www.wwu.edu/huxley/spatial/tut/cart/cart_rules.htm 

Cartography is as much about style and artistic design as it is about information and communication. Try to keep in mind both of these goals (style and communication) when designing maps. While there are very few hard and fast rules for cartography, there are many standards or conventions that are widely adopted. Taking advantage of these commonly recognizable standards will generally make your maps more readable for your viewers. Thus, while the following are by no means rules that must be followed, they are found on many maps...

There are a number of commonly recognized symbols that can be taken advantage of:

Point Symbols

                     

    Capital         Schools         Hospital  Marina

     

Line Symbols

                           

    Rivers     Highways    Interstate    Internat.    Railroad

  Shorelines                                     Border

  

Polygon/Area Symbols

                

        Oceans     Forests   Wetlands

         Lakes

Text and Annotation

    Natural Features: Italics

    Human-made features: non-Italics

    Hydrology features are often labeled with Blue Italic text

        If for a river, text should be 'splined' (follow the line of the river)

    States and/or Countries are typically labeled - non-Italic, bold

    Major Cities are typically labeled - non-Italic

    Avoid crossing feature lines with text (add a 'halo mask' text if necessary)

    Mountain ranges typically have splined text following the range

        Mountain ranges often use wide spaced lettering

    Text can be horizontal or rotated up to 90 degrees or down to 85 degrees

        Vertical text should read from bottom up, not top down

Legends

    Not all layers in a map need to be included in the legend. Examples of layers you might choose to leave out of the legend:

• Water, which is typically understood to be blue and easily recognized
• Raster imagery (Air Photos or Satellite Imagery) whose nature is self-evident

            Such imagery should, however, be listed in a data note or the like, listing the date and source of the image.

General

    Use even numbers for Scale (1:200 or 1:2,400 as opposed to 1:243)

    Zoom in to the area of interest.

    Avoid showing areas beyond the available data (or areas with only some of the data layers)

    The human eye (and the common printer) can only differentiate between a few shades of any one color (do not attempt to have 6 shades of red or 8 shades of green). The exception to this is in the case of a color ramp where the purpose is to indicate a gradient of many colors (in which case the viewer is not expected to need to or be able to precisely identify any one color).