As a teacher you should always try and leave your classroom so that someone else could come in and teach if they need to. You should have lesson plans for at least the next week ahead but ideally rough plans taking you up to the next half term. You may not always know if you are going to have to have time off so it’s important to prepare and be organised. If you do know that you are going to have to have time off then you can get work prepared to leave for a supply teacher. Ideally try and have a chat with the supply teacher so you can talk over your lesson plans and explain what you want them to do. This also gives them the opportunity to ask any questions they may have.
You may also want to give them an overview of the class such as if there are any pupils they need to keep an eye on or any that may need extra support.
If you need them to mark work then make sure you ask them to do this. If it is a supply teacher that has not worked in your school before it can be useful to write them a quick list of useful information such as break times, names of other teachers that teach that year group or subject and details of the teaching assistant who will be working with them.