Every school should already have an ICT Acceptable Use Policy that is agreed by all pupils. You may wish to review this and revisit it with pupils prior to your 1:1 launch.
Prepare a home/school agreement. This is a document that sets out clear expectations and procedures for pupils, parents and the school, and should be signed by all three parties to indicate agreement with the terms.
When implementing 1:1, it is even more important that pupils and staff are clear about how to be safe online. It is essential that schools have a well-structured digital safety programme with appropriate curricular input at every level. The Digital Learning Team have produced digital safety resources you can use here. Regular briefing sessions should be organised for staff, possibly supported by Child Protection staff.
It is important not to underestimate the importance of day to day discipline and technical procedures in a 1:1 deployment. All school staff should have a clear understanding of what actions to take if any issues arise and these should be shared and discussed well in advance of your launch night.