If you are a contractor I’m assuming you work on large projects, hopefully you have an external document that your customers sign prior to work starting. I typically add a service in Jobbers products and services that references the external document and/or general terms of service hosted on the company website.
If you are still building your formal contract document I would reference one that you have signed when hired by another contractor in your area/field. If it is a large company they have likely paid attorneys to review and fine tune the verbiage to legally protect them.
yours may not need to be as in depth but you can change the wording to what you do and offer.