You can ask them how they define certain roles - we all perceive them differently, there is no one way of doing things in BDSM, so verifying whether their definitions are compatible with what you need and / or want is crucial.
You can ask them about their limits. - we all have limits, and claiming that someone has no limits, should rise your attention, as it might be a possible red flag.
Ask them questions not related to kink - it will allow you to know the actual person, not only kinky side of that person. It might also be a nice way to see who is in a rush and not really willing to take their time to know you as well.
Important thing to remember is that asking questions is one thing - at the beginning most of people wants to present themselves in the best possible way, so it might be tricky. But actions speak louder than words - try to observe how (if ever) they interact with other people here.
But also... take your time. I know it is probably the last thing you might want to hear when everything is new and exciting.
First of all, take your time to talk to people, both Dominants and submissives - it will give you opportunity to listen to different point of views and different opinions. Ask as many questions as possible, even ones that you might think are silly - the truth is that there are no silly questions. This will also allow you to make friends, and those are priceless in the lifestyle.
Secondly, always listen to your gut. If something does not feel right for you, then it probably isn't. If someone tries to convince you that "a real submissive" would do this or that, remember that there is no such term as "a real submissive", we are all different and have different needs (and that's OK).
Thirdly, keep in mind that at any stage you have the right to say no. Everything should be consensual. What is more - your "no" should not be perceived as something bad.
And last but not least... don't give up. It might take you some time to find someone suitable for you, but that does not mean you should settle for less. Hell no!
Good luck