example_module_for_including_in_an_active_record_model.rb

module ModuleName
  include OtherModules

  delegate :some_method, to: :some_object

  module ClassMethods
    def class_method
    end
  end

  def self.included(klass)
    class.extend(ClassMethods)

    klass.instance_eval do

      has_many :...
      before_create :some_method
    end
  end

  def instance_method
  end
end