I have been camping pretty much every year for the past 30 years. I am getting quite good at it now.
My biggest tip, and I only discovered it a few years ago, was to take hot water bottles. So easy to heat up some hot water before bed and it makes such a massive difference in the sleeping bag. But I agree with pp, extra blankets or fleece liners are well worth it. And hats make a massive difference. Nice pillows are worth taking. Until recently, dh and I took sheets and our duvet but I have woken up too many times where he has pulled it off me in his sleep so have reverted to a decent down sleeping bag. The mattress you use makes a difference too. Air obviously insulates well from the cold ground. The cheap inflatable ones are fine for the kids but not very comfy for an adults weight. We invested in some self inflating foam and air ones but sadly they are not cheap. I have spotted decathlon have a version which is cheaper than the vango/outwell ones though but I consider my outwell dreamboat bought about 7 years ago worth every penny I spent on it.
Also agree with slip on shoes for night time/early morning troping across fields to the loo. Even in good weather the grass gets damp from dew and so crocs/sliders can be good but I'm also a fan of a low, easily slipped on welly boot.
I also like to take something to use as a washing up bowl. I now have a collapsible one to take up less space in the car but I have used storage boxes in the past- it's handy to throw all the dirty stuff in and use it to transport the dishes/cutlery/etc to and from the washing up stations too.
I don't waste money on those water carriers but just always buy a big water bottle each trip and refill it from the taps once empty.
Head torches are brilliant (again v cheap at decathlon) but a lantern for inside the tent is v useful too- doesn't need to be massive but it's really helpful. Or sticking a small torch into a an empty milk bottle makes an instant lantern!
Take a roll of duct tape with you as its uses are endless! And a few carabiners and some spare twine/cord come in handy too