Acceptable Use/Internet Safety Policies are usually provided by the district. Here is an example from my local district:
This publication offers "guidance and food for thought" from the Association for Library Service to Children. It includes sample internet policies.
This is a guide from ALA that includes the full text of CIPA, as well as background resources and FAQs.
This is a guide from the NJ Department of Education (DOE). The "filtering" and "Acceptable Use Policies & Guidelines" are largely outdated, but the "General Information" section has some current content, and the sidebar contains additional relevant resources from the DOE.