The modular system is what makes POLY unique, but how exactly does a GM use it to create the game world they want to play in? First thing to remember is that most game systems spend 95% of their time trying to invoke the feel and mood of the game through rules, why trying to maintain a sense of realism relative to the level of play. POLY lets you do this with your own game, but allows for each setting to modified and readdressed.
The first major decision facing a new POLY GM is to decide on the highest level they're willing to use. This is not a hard and fast decision, as some of the rules at a any given Level may be appropriate while others may very well not be, but in general, a setting should suggest an upper level by it's very nature. Cartoon, comedy and pseudo-real worlds found in Japanese animation and comic books should be limited to levels 2 or 3, while more complex worlds, like the ones in most rpgs and popular fiction will be looking in the 4 or 5 range. Level 6 is geared for ultra realism, and should be reserved for gritty or hard genres like hard boiled detectives, film noir and hard science fiction.
Class on the other hand, is not a setting specific decision but a stylistic one: How many rules do you like in your game? GMs who don't like dice or rules should keep their eyes on the first three classes, and keep notes for abjucating all in play variables, including pain and damage. This isn't generally as hard as it sounds.
Next, character creation can be a trick subject, especially if Sub-Abilities and Personality traits are thrown into the mix. Generally, Skill lists should be kept narrow if your also using Specialities. Levels should only be used in games that have inherently diversified characters, and simple, quick leaps in power. Levels will probably take a lot of the character's focus. Using all Levels, where each character is simply a level, is a reasonable option in games that are either highly abstract or highly realistic, as long as levels are generally hard to adavance. Abilities, Level and Speciality is also a workable combination for players who wish to avoid Skill lists and long character creation times but find flat levels to restrictive (outside of 'special powers' D&D works on this system (a fighter, for example is a Level X character with a Speciality in combat, and a varying Strength, Dexterity etc...). Special powers are generally handled as Skill or Abilities despite the systems being used, and thus Levels can be a good choice in games that focus on supernatural powers (DBZ comes close to this, with POWER working as a 'Level' while the character learns special attacks).
