I don't think there is an official guide for conducting tournaments at this time, and the rules have changed slightly from tournament to tournament. The following are the most recent tournament rules that I am aware of being officially used.
Swiss Style Rounds: If you are unfamiliar with how these work, you can read more about them
>>>here.<<<Points: At
Bashcon they awarded 3 points for a Win and 1 point for a Tie. In addition, they gave 5 tie breaker points if you finished before time was called and 3 tie breaker points if you got a timed victory.
Time Limit: I would recommend granting as much time as logistics will allow, based upon how much time you have available at the venue and how many rounds need to be done. The upcoming
Origins Tournament will have 75 minute rounds, which I think is acceptable. I would be hesitant to do less time than that, and 60 minutes would be my absolute minimum. If you do not have enough time to allow rounds to be at least 60 minutes, then you may consider holding the tournament at a different venue, or on a different day, or breaking it up over multiple days.
End of Time Procedure: Looking again towards
Bashcon the end of time procedure was to finish whatever round you were on and then award victory to the player with the most life remaining. If the two were tied on life, then they would play another round, however it would be equally valid to simply declare it a tie at that point if you are pressed for time. There is some controversy over this tie breaker method, and you can find alternate suggestions among the forums, but this is the current official method that I am aware of.
Legal Spellbooks: Every official tournament has used the standard spellbook rules for a 120 point spellbook with the following exceptions. Promotional cards have not been allowed, and restrictions on which sets of cards may be placed. Typically players are required to register their spellbooks before the tournament begins.
Here's an example of how you might register the spellbooks. You might also require mages to bring their own mage specific ability markers (ie Pet, Voltaric Shield, Deflect, etc) as otherwise you may find yourself in short supply if a surprising number of people decide to play the same mage.
Arena: The full 4x3 arena is used in every official tournament, but there is nothing stopping you from modifying this. Just make sure you advertise that you will be using a non-standard configuration so that nobody is surprised. If you decide to do an Apprentice Tournament and use the 3x2 arena configuration, I would suggest changing the spellbook rules as well. Either limit them to only the 4 pre-built apprentice books, or try your own version of Apprentice Spellbook Rules. I've experimented with the rules as follows:
1) 60 Spellpoints
2) Limit of 2 copies per card
3) No Zone Conjurations. Conjurations which attach to creatures are fine.
4) No Familiars or Spawnpoints
These rules can drastically altar some mages strategies, specifically the Druid. She feels very similar to a Beastmaster without her conjurations. Also, remember that in Apprentice Mode the mages all have 24 Life, 10 Channeling, and No special abilities.
Your Tourney, Your Rules: In the end, you can run the tournament however you see fit, guy. Just make sure you advertise all of the details so that nobody feels like they've gotten a nasty surprise. The most important thing about the whole ordeal is that people have fun. Try to make it as memorable as possible, show people a good time, and it will be a success.