My random bits of advice from my experience doing this:
What you should require/ask varies considerably with how selective you can be, which in turns varies with how quickly you need to find someone, the desirability of your location, your tolerance for risk, your tolerance in general, etc. So the first thing I would do (after determining that your lease allows roommates, and the necessary procedure for adding them) is assess how long you can hold out for the right roommate and how important it is to find someone who is stable/compatible. If you plan to require credit reports, for example, you might end up waiting longer to fill the space.
In general, I think you’re trying to avoid two big problems: roomies who can’t pay rent and roomies who are crazy. Avoiding the first is a good bit easier than avoiding the second. The four basic things to require, in an ideal world, are a credit report, proof of income, contact information for prior roommates, and at least one in-person interview of significant length (coffee or tea). (Research suggests warm drinks cause people to trust you, making them more likely to be honest.) I don’t think it really matters what you talk about in the interview. Obviously you want to ask about cleanliness, smoking, sleep habits, etc. But I think the main point is to assess the person’s mental state, which is probably best done by talking about stuff outside the normal questions. Together those things should be able to steer you clear of most problems. But you might have to settle for less if you’re in a hurry.
You also need to consider how you want to structure your relationship. Will it be month-to-month? That has the advantage of being able to get rid of a bad roommate easily, but also means a roommate can leave you looking for someone new on short notice. Again this is probably a variable of your financial need and your tolerance for crazy people.
Good luck.
p.s. I’m sure you already plan to do this, but just in case you hadn’t thought of it, be sure to draft or fill out standard form laying out the roommate relationship, including use of utilities, who pays for utilities, when rent is due from the roommate, responsibility for damage, termination of tenancy, household chores, guests, results of involuntary termination, smoking, pets, etc. Have it in writing!