Roots from plants in pots can be damaged by frost, so if they’re too big to bring inside, use bubble wrap around them, or hessian, which is a bit more attractive. Gather pots together to give mutual protection, and place near a wall away from sharp winds. Make sure your terracotta pots are truly frost-proof, as many will not be if they’re labelled frost resistant.
You can cut back perennials and divide congested clumps, but leave about 15cm of old growth to protect the crown of less hardy plants and prevent winter damage.