Internet is, in my opinion, a human right. If the teenager is making money, we could discuss them contributing to the internet bill, but internet is too important not to have.
Own Your Possessions
Possessions shouldn't be confiscated, especially not ones the teenager needs, e.g. laptop, and especially not ones the teenager bought with their own money. This is the flipside of teaching that actions have consequences - what's the point in spending your own money on something if it can just be taken away by a higher power?
Any teenager in my hypothetical house is expected to get exceptional grades. Whether it's on brute intelligence or on study, I don't care - although they'll have to learn that raw intelligence stops working when it gets tough, and by that time they'll need to know how to study. But whatever - exceptional academic stats are expected.
Books are heavily praised, as is learning of all kinds. Learning for its own sake is encouraged.
As the teenager grows older, gradually stop stepping in for them all the time when they screw up. When they really need you you should be there of course, but they need to learn how to support themselves.
Sheltered teenagers are the worst. It's important to get out there and live your life, and if the teenager is responsible and can fund their own trip out for the day, you should be biased towards saying yes. There are always going to be times it's not possible, but at least be open-minded.
Don't Respect Your Elders - Or, Equally Valid Opinions
Your time of landing on this planet doesn't make your opinions more or less valid than anyone else. Older people might have more experience, sure, but by the time you're a teenager (15+) your reasoning faculties are developed enough to have a sensible debate over something. It's unfair for an adult to veto things just because they can. Adults need to open themselves up to being wrong
Lying is a serious transgression, because it destroys trust. Create a house where there's no need for a teenager to lie to their parents, because they don't have to be afraid of a bad reaction. This doesn't mean letting the teenager do everything, but it does mean keeping an open mind and being open with each other.
No Drinking/Partying (Within Reason)
This is something the teenager and parent should discuss, and there definitely has to be a degree of trust between them. But at least until a certain age, just point out that drinking/smoking/crazy partying aren't actually that cool, that it's not worth damaging your future for, and there are other ways to have fun.
Base Rules for Chores
Said "Chores" for the benefit of you Americans. It's much more predictable for everyone if there are rules. On the other hand, the teenager(s) should have initiative and recognise the need to help around the house. But almost everything should be negotiable, because life screws up sometimes.
Accept Each Other
This goes both ways, but primarily from parent to teenager. If the teenager is LGBTQ or something, don't be an ass about it. Parents, try to understand.
Teenagers are people too, and everyone deserves privacy. Sometimes they don't want to talk to a parent about their day, because their peers are more likely to understand. That's why they're peers. Accept this.
Encourage Going the Extra Mile
Encourage curiosity. Encourage hard work. Encourage shooting above average, punching above your weight, proving people wrong. Teenagers should have initiative and be able to devise and complete projects. This is a valuable trait to have in life.
You may have noticed that this list is low on punishments or forbidden things. That's partially my bias, but also because - using myself and my friends as a template for the teenager - they should have some sense.
Also, to have a household this perfect would require robot parents, and I don't know if I could accept a non-intellectual child, so I'd make a bad parent.
But yeah. Those are my ideal ground rules.