It is recommended to write up a contract. Having it in writing with there signature is the best way, then they can never say that you never told them. List the rules but keep it simple. Then also list the consequences if a rule is broken. ** You must be willing to follow through !!!}
Yes you can also put in the drug test. But like most of us whom have done that you will soon learn the the tests get expensive. Keep in mind the consequences must follow immediately.
In my house there are three simple rules 1)No drugs or paraphernalia of any kind. 2)Help do choirs around the house (cleaning, laundry, cooking, dishes, mowing lawn, etc.) 3)Have a job and pay rent of 100 a week.
Breaking any of the rules you are out of the house by sundown.
Keep in mind I have been dealing with my 2 AS's for 15 years, at this time only one is staying with us.
Everyone has there own list, and there own way to keep harmony in the house so keep it simple and you can talk other issues out as they come up.
Hope this gives you some insight from someone that has had a lot of trial and errors before finding something that works. To each there own, though what works for one might not work for you.
Be well,