Brad's "Rules for Origami" -- These are the guidelines I try to use in designing boxes, bowls and vases.

1. No "extra folds" -- when a design is complete, there are no mountain or valley creases out in the middle of a plane.  All creases are used to construct the design.  To do this, I usually include all folds necessary the first few versions.  Then I mark those "extra" folds, and go back to the beginning, to see where they can be eliminated.  Usually it means just making a light crease for a landmark and folding to that point.

2. No "raw edges" -- the sharp edge of the original paper is concealed if at possible.  Some of my early designs don't follow this rule.  Others bend the rule by having the raw edge nearly concealed or abutting to a perpendicular wall.  To me this rule just makes for a more elegant model and a more finished look.

3.  Choose the paper wisely -- A finished model should generally expose the origami paper in an interesting way.  A two-colored paper is preferable usually, and if a pattern is present, it should complement the design of the model. It's fun to try the same design with different paper. 

4. Practice -- A finished model should not look "tortured to death".  The first few times making a model (or following someone else's designs) it may look a little rough.  But after you've made the model several times, the folds should look crisp and neat.  I think it's fun to go slow and thoughtfully. 

5.  Process -- Some designs are more fun to fold than to enjoy afterward.  Some of my rectangular boxes definitely come to mind. Why would I want to make yet another rectangular box?  Indeed, some of my boxes look very similar to one another, though they are each constructed differently.  Conversely, some models vary only one or two folds, but the results can be quite different.   I think the enjoyment here is definitely the folding process, and discovering (or rediscovering) the thought process that went into the design.

6.  Elegance -- this is a more esoteric goal, but the model should conform to basic rules of conformity, balance, and continuity.   The box should hold together on its own and not flop open or lose its shape with reasonable handling.  Since I mainly construct "containers", I think its reasonable to think about what the model could contain (pencils, M&Ms, business cards, paper clips, etc.).  I'm not a super-duper artiste (arteest), or mathmatician so I am completely amazed by models by the Shumakov's,  Joseph Wu, Gilad, and others. 

7.  Instructions -- the art of good diagrams is quite a challenge!  What makes sense to me might not make sense to you.  Sometimes I can't follow my own directions after several months!  So I try to make clear diagrams with good explanations.  I don't succeed, but I try.  I have spent countless hours trying to follow the cryptic diagrams of noted designers, even jumping across language barriers when I exhausted all the English-language websites.  I ask friends and family to try following the directions of my diagrams.   Diagrams should conform to the generally accepted standards (as to symbols and terms).  I like to see if the diagrams alone (without written instructions) are clear enough to allow one to successfully complete the model.