It's important to be compatible on a couple of things:
Hours you keep: If one of you is a teacher who has to get up at 5 and the other is a bartender who gets home at 4, it's not a good idea to live together
Cleanliness: One messy vs. one with OCD = issue
Guest Policy: Do you like to have people over (even if just to watch tv)?
Budget: Make sure you both can afford to pay rent, utilities, AND eat. If your budgets aren't compatible, don't live together, no matter how great the place is
Do you LIKE each other: This is a big one people seem to forget. When you meet your potential new stranger roommate, do you like them?
*This was voted the best answer from our community of users, not an answer, opinion or advice from HotPads.