Using a Google search for "The Rules of Hidden Club," I found the document you're looking for as the first result.
It's essentially an explanation of the rules for the Stealth skill (found in the Rules Compendium or on the Compendium website) with a guide to applying them wisely.
The basics, heavily summarized, are:
The First Rule Of Hidden Club: Stay out of sight. If, at ANY TIME, you lack at least Cover or Concealment from an enemy, you lose Hidden against that enemy.
The Second Rule Of Hidden Club: Keep quiet.
The Third Rule Of Hidden Club: Keep Still. If you don't move more than 2 squares at a time, you have no chance of losing Hidden.
The Fourth Rule Of Hidden Club: Don't Attack. If you attack, you are immediately Expelled From Hidden Club, period.
The Fifth Rule Of Hidden Club: Don't let the enemy FIND you.
The Unspeakable Final Rule Of Hidden Club: When you do something to lose Hidden, you keep the benefits of being Hidden until the end of that action.