It can be a BLESSING because you can do what you like. Yahoo! Before you get too carried away and launch the fireworks, find out who the class captain is to whom you can direct all the initial questions - where the class roll is, what does that bell mean, etc.
Pull out your favourite reliefteaching.com lessons that you have downloaded from this site.
I suggest you only do work in the MATHS BOOK (every teacher has a MATHS book) or an ENGLISH book (sometimes called a LANGUAGE book).
Teachers appreciate when you check, sign and date all work you complete during the day. It also sends the message to the students, that you care about and will monitor their results during the day. Don't hesitate to pull up students for inadequate work.
It can also be a CURSE because you really need to know the procedural activities of the day such as - when the kids go to specialist lessons, which kids are needed to go to where and when.
These can spoil your day if you don't know, so check with someone early in the day about these issues. Sometimes the office staff can provide this information, sometimes you need to check with your teaching partner.