1. Set the standard.
While this will extend outside of the first week, remember that you never get this first week back. It's important that you rehearse routines, and I mean that in the most literal sense. Get up, show them where you want them to go, and repeat. The likelihood is that they'll be performing many of these routines on a daily basis, and you don't want to keep explaining it.
2. Find the standard.
Yes, you'll have been given some kind of data towards the end of last year about the class being sent your way. But it's important to find out what your starting point is for the year. I've learnt to never assume, and I've discovered the importance of creating common ground, even when it comes to the basics. I think there's great power in being able to refer to 'the lesson you taught them that thing', even if it's supposed to have been done before.
3. Be flexible.
On one hand, there's a safety in over-planning the first few days, it means that there's always something to do. But sticking too rigidly to what you assumed was possible, means you end up with 4 incomplete projects, rather than 2 or 3 suitably crafted products. Be prepared to change what you had envisaged - and don't forget to take time to talk with your students.
4. Be equal.
Not only is this a great time to set standards and routines with your class, it's also a good time to do it with yourself. Decide, when possible, what you'll get done and when. Overtime, you'll learn to prioritise, and it all takes experimentation. Consider at what points in the week you need certain books, and match that with when you're going to mark them. Additionally, think about the order in which you plan your lessons; preparation takes time, and there are only so many hours in the day.
5. Don't hide.
It was a few days into my NQT year, during a lunchtime, when I vividly remember eating at one of the children's desks. Alone. Likely feeling overwhelmed, or too scared of the staffroom. A couple of teachers came looking for me, and told me to stop being so ridiculous. Of course, it's different if I had been using that time productively - but I wasn't. Your colleagues are important, the only ones that really know what your day is like. Take time to talk - doesn't have to be lunchtime - and get to know one another. It's a family.