Ideally, good discipline is established when children are young.  But there are parents who have let their children run the show and now can’t understand why their children ignore them and refuse to obey.  I’ve heard these parents say terrible things about their children as if it was their child’s fault.  Of course their are exceptions.  Some kids may become undisciplined even though well disciplined as younger children.  (This could mean drugs or bad friends.)

Here are a few suggestions.

1. Take the first opportunity you have to sit down and talk to them.  Make sure neither of you are made at the other.
2. Let them know you love them and you realize you’ve failed them as a parent.  (This is one of the things I mentioned before.  Admit mistakes)
3. Explain that teaching them discipline is an important part of parenting.  Apologize to them for not having done it.
4. Further explain that teaching children to be disciplined adults is important for the children, and in this case, young adult children, to succeed in the world.
5. Wait for their response.  If they say nothing, ask them for their opinion.
6. Rather than you deciding what rules you want them to follow, work with them to develop some rules that you can both live with.
7.  Once the rules have been established, decide upon consequences you can both live with.  A good idea would be to make a contract with them.  You and he/she write it out together and sign it. This way either of you can pull out the contract if either side violates it.

I can’t say this is a perfect solution, but given the situation, I believe it will work with some tweaks.  Keep in mind, no one thing is perfect, it needs to be reworked as necessary.  My suggestions are merely a framework for you to follow.