Organisation is key - and it needs to be directed by then not you.
Start now - what day do they take X to school? What day is the deadline to return X to school or pau for a trip? Help them with structure like drawing up a timetable to stick on the wall or working out other mechanisms that can help but don't save them from messing up.
Far better they learn at 10 or 11 or 12that there are consequences to failing to organise themselves than when they are revising for GCSEs.
Better they get a detention or miss lunch break or whatever for forgetting their PE kit now than fail to revise for their exams at 16.
Don't argue over small things like them wearing a coat. They won't actually freeze to death, they'll just be uncomfortable and learn from the experience.
Talk to them proactively about things like phone use and it's link to mental health, porn etc. Maybe find an article in a newspaper to help direct the conversation. Keep talking to them about it - regular small talks not one big one off!
Encourage them to invite their friends round. Have lots of snacks in the house.
A lot of girls stop doing sport in secondary school - boys are still having a lunchtime kick around but girls are not running around. Encourage/facilitate activities like yoga or dance or running out of school if they aren't into traditional team sports. It's much harder to get back into activity as an adult.