A List Apart: Reading Design contains this splendid list:

An Entirely Incomplete List of Things a Non-Illiterate Designer Should Know Before Being a Designer:

• That text will inevitably be read before it is looked at
  
• That words themselves make remarkably effective clip art
  
• That the self-conscious layering of messages usually subtracts more value than it adds
  
• That the practical value of white space towers over its value as a design element
  
• That the deep symbolism of a design decision, referring perhaps to a treasured memory of the designer, is irrelevant to the person attempting to glean something from the work
  
• That print designers who gauge their work on the screen, and web designers who gauge their work exclusively on their own machines, are arrogant in their disregard
  
• That the physiobiology of reading is one that demands easy points of exit and entry
  
• That simply paying attention to the design of type, or distinguishing it as "fine" or "invisible" or "classical" is like making a big deal about putting salt on a boiled egg
  
• That letters are not pictures of things, but things
  
• That words are not things, but pictures of things
  
• That arbitrarily altering (or allowing software to alter) the shapes of letters, and the spacing between letters and words, is done at one's own risk
  
• That emphasis comes at a cost
  
• That overstating the obvious can be effective, but not all the time
  
• The precise point at which a quantity of information no longer requires assistance to be differentiated from another
  
• The knowledge to back up design decisions clearly without falling into a fog of hidden meaning, or so–called “creativity”