Our rules were very simple and easy to follow. The child had to either be in college or working full time and paying some rent (trust me, nothing earthshattering). They had to be respectful and do some minor chores (keeping room clean, mowing lawn) and not breaking the law. We didn't give them a curfew, but if they were going to be out all night or late they needed to leave us a message about where they were so that we didn't worry and they needed to be there if we called...so I'd say honesty was important. They also had to pay their portion of car insurance, whatever the extra fee was that made our insurance higher...where we live that could be maybe $50 month. Nothing illegal in our house.
Unacceptable was any illegal activities or any sort of abuse toward other family members or not going to school or working (one or the other). In other words, you can't just lay around the house, eating, watching TV, texting, etc. No pot in our house or other drug use, no coming home drunk repeatedly, no swearing at us or calling us names or assaulting us or destroying our home. Swearing was fine. Using it at us was not. "I had a b**** of a day" was fine. "You are a b****" was not ok. We didn't call them names and expected them to reciprocate the favor. My kids did not smoke, except for my daughter for a few years. Smoking in our house was forbidden so she had to smoke outside. I don't know if she always did, but smoking in her own room would not have made us make her leave, however it would have been addressed.
Amazingly, two of my kids couldn't do it. My daughter turned to drugs for a while (thankfully she has quit) and 36 was scary and abusive and,a lthough he did not do drugs, he liked to steal and was a good thief and he was a threat to my daughter, who was then only eight years old.