It would be best to always assign an assessment to a page following the Assessment guidelines at WP:MLA/A. For the quality scale, it's usually okay to go with whatever is present on the other WikiProject banners. If there are no other WikiProject banners, the criteria are typically easy to understand and apply. For the importance scale, applying the criteria isn't that easy most times. In this case, it's best to create a new topic within the talk page or to contact one of the project coordinators.