From a teachers perspective ...
Get them in the habit of packing their bag the night before - every night.
Teach them not to be offended when teachers don’t learn their name straight away. I teach the whole of year 7 (150 pupils) once a fortnight. Takes me nearly all year to learn their names!
The older pupils are actually nice to year 7’s despite what people may think (I work in inner London - our pupils really do help the little ones)
Take lots of snacks for week one at least. The lunch queue in the first few weeks is always very slow! Even when most schools give year 7’s early lunch they will spend half their lunch in the queue
Label everything with sew in labels. I always find jumpers / bags etc in the playground / my classroom with no label or washed out felt tip pen labels you can’t read.
Get them a pencil case with basics and make sure they have spare pens in their bag. ‘I haven’t got a pen’ drives teachers crazy!
Check what is expected with their planner. Most schools ask parents to sign a planner weekly and will give detentions if it’s jot signed. Use it to check what homework they have etc and for any notes. If you wrote a note to a teacher in a planner, ask for a signature to confirm they have read it. Your child probably won’t show it to their teacher unless prompted!
And as a parent be aware that contact with school will be different and give teachers time to respond to emails or calls. In total I teach around 260 different children each week. So while I try to respond to parents sometimes I am very busy so it’s a quick reply. And if it’s something your child can ask the teacher - get them to do it. If a child doesn’t understand their homework, it’s much easier If they come to see me rather than me trying to explain it to a parent via email.
Get them to join some clubs. Most schools have loads at lunch and after school and there will be something for everyone. It’s a great way to make friends in different classes and years too.
Make sure they know to go to the toilet at break or lunch. They won’t be allowed during lessons (unless it’s an emergency of course!)
Most pupils settle really quickly. A few struggle to check in with them and contact the school (form tutor usually) if you feel your child is not settling after a few weeks. We have lots of strategies in place to help pupils that work.