Once the team is formed and functioning effectively, the first and foremost task of any PBIS process is to define, in positive terms, the behavior that is expected. The broadest sense of these are the behavioral expectations - three to five terms that encompass the types of positive behaviors you'd like to see. Examples might be: Respect, Responsibility, Safety, Participation, etc (as nouns) or Respectful, Responsible, Safe, Involved (as adjectives).
Some schools and preschools develop a slogan that is tied to the behavioral expectations to make them more memorable and fun. Some examples are the "ABC's" (Act Responsibly, Be Respectful and Care and Cooperate) or "The BBD's (Be Safe, Be Kind and Do the Right Thing) or "Do Your BEST" (Believe in Yourself, Extend a helping hand, Show respect and Take responsibility).
Put some thought into the expectations. They will guide everything else you do and they provide a chance to make PBIS your own with a motto, a slogan or a tag line that is unique to your community.
Please do not be tempted to use a long list of character traits as your expectations. Stick to at least three and no more than five. More than that will dilute your efforts.