1. How often do you have guests over?
Often overlooked, guests and overnight guests can drive you insane. At the very least, be sure to put some restrictions on overnight guests. Otherwise you may end up getting two roommates for the price of one.
2. How noisy are you, overall?
If you're trying to sleep and you've got a roommate that slams doors and is playing loud music late at night, you're going to be miserable. The best advice is to get a quiet roommate. If not, at least have some agreement regarding quiet hours.
3. How often do you do laundry?
Laundry is not just noisy, it can get expensive if they're doing it every day. Let alone all the extra clothing you'll be seeing left in the dryer for someone else to empty. There should be some kind of agreement made in advance, regarding laundry use and hours.
4. How would you rate yourself regarding cleanliness?
Ask about the dishes, kitchen, refrigerator, items laying around, pet hair, etc. Cleaning up after others will get old real fast.
5. How long do you plan on being here?
If someone is looking for something really short term, remember that you'll be looking for another roommate again soon, and up goes the cost of vacancy.
6. How often do you cook?
This is another overlooked question. Some people insist on cooking every night, and there's the possibility they'll be hording the kitchen, smelling up the house with food, and probably leaving dishes and utensils everywhere – while driving up your gas bill.
7. How much stuff (junk) do you own?
If this question is overlooked, you may end up with someone that crams your house and garage full of items, until you have no room left at all. The best option is to have them rent storage space instead of bringing their own junkyard to your home.
8. Are you willing to take out the trash and help with other duties?
It's best to get this situation squared way sooner than later. Imagine a trash can that does not get emptied, or cans that are not taken to the curve. You may end up doing all of this yourself unless you have an agreement in place.
9. How stable is your job?
The worst situation to avoid is someone that does not have a stable job, or even a car to get to their job. They'll end up not making rent, and then you'll have a serious problem on your hands.
10. How timely are you with making the monthly payments?
Believe it or not, almost every roommate will at some point be late with the rent. Some will pay late habitually – and this is what you want to avoid. Let them know that you expect it on the 1st or sooner, and that you do not like having to ask for it. Also, be sure to collect first and last month's rent upfront, and possibly a $ 200 refundable deposit in case of any damages.