How to name variables

Question

• What rules do you use to name your variables?
• Where are single letter vars allowed?
• How much info do you put in the name?
• How about for exam

Answer 1

function startEditing(){
   if (user.canEdit(currentDocument)){
      editorControl.setEditMode(true);
      setButtonDown(btnStartEditing);
   }
 }

Should read like a narrative work.