The Rules of Tangling ...

There are no rules ... period.  

The Zentangle motto, "Anything is possible... one stroke at a time," sort of emulates this ... In searching, joining several groups on FB, scanning and "pinning" on Pinterest, and looking at other's work I've had an epiphany (several actually):

• Basic tiles are 3.5" or 4.5" white/ecru squares (and sometimes black or renaissance/tan) - but it's OK to do something on 5X7 (or another size)
• There are also a variety of other sized "official" tiles - Bijou, Zendalas, Opus
• Tiles are a specific type of paper - but it's OK to use a good quality watercolor or cardstock paper - in other colors - (not to mention a large variety of 3D items in wood, ceramic ...)
• A "string" usually leaves a little space from the edge before starting the patterns - but it is OK to take your work all the way to the edge 
• The string is done with a pencil, freehand, doesn't need to be perfect and doesn't get erased - but is is OK to erase if needed, and if you want a really straight line ... use a ruler
• The string line can be inked in or left "invisible" - but it is OK to also enhance it with an aura or pattern
• Most sections of a string are completely filled in - but it is OK to leave open space(s)
• The basic black pen is a Sakura Micron 01 - but it's OK to use other brands, colors, types, and sizes for certain effects
• Patterns:  There are the "official" patterns created by the originators, there are patterns that have been submitted by the many CZTs ... there are patterns that have been inspired by other patterns (maybe sometimes by making a mistake) ... there are combined patterns - called "trangulations"
• Shading - optional (but it can really add depth and texture)
• Color - optional
• Oh, and there are no mistakes either.  As Scott Adams has pointed out, "Creativity is allowing yourself to make mistakes. Art is knowing which ones to keep."

Feel free to add your thoughts / epiphanies about tangling in the comment section ~