Both our DDs are at university now, but have very rarely (if ever) given us any cause for concern. They're both just really lovely, decent girls and I genuinely love spending time with them. I think they must enjoy my company too because they regularly invite me along to stuff they're doing. What really helps is that we all share the same sense of humour and enjoy doing the same things.
Anyway, here's my parenting blueprint.
From being very little we never tolerated bad behaviour from our DDs, even small infractions were questioned and swiftly dealt with.
Always be aware that what children want and what they need are two very, very different things.
Fair but firm boundaries. Children need (and like) this. It makes them feel safe and secure. Say what you mean and mean what you say. No faffy, touchy-feely parenting where no one knows where they stand. No empty threats, constantly changing the goal-posts, or giving in just because it makes your life easier for the next 5 minutes.
As teenagers, I never had a problem with them lying in at the weekends. I never, ever limited their screen time - because I made it clear that if their grades started to drop at school as a result, I would remove their screens. So they never risked it. I always respected their privacy, never went snooping in their rooms, never eaves-dropped on their chats (my Mum did all three and I hated it).
Told them every day that I loved them. Hugged them often. Complimented them regularly.
Finally, they knew it was my job to always be their Mum, and to always look out for their best interests. It wasn't my job to be their best friend and let them do whatever they fancied, and just tell them what they wanted to hear. I take a very dim view of Mums who brag that they're best friends with their teenage daughters.