Are you looking for a center or an in-home place? Either way, you'll want to do your research and find out what other people have said about them...ask for references, and call those people. Ask what they liked and didn't like.
Our in-home sitter (at her house) was FABULOUS! Our youngest son (6) was the only one who went there full time and he did that for a year and a half, he chose to go to her house for a "camp" this last summer instead of another actual camp...we love her.
We asked her what all of her policies were, most are laid out and then your questions will come from there. Ask other people what they don't like about their daycares, and ask those questions of your provider. For example, a friend of mine's sitter (in-home) closed on school snow days...that's crazy, because in MD they close all the time, even if it is only raining! So they took a lot of leave to cover those days.
Ask about time off. I disagree with NewName2013 about the time off though. My sitter gave herself all of the Federal Holidays, plus 10 days of leave. Yes, it was a lot and it sometimes caused problems for us, but she also took 5 of those 10 days in a week, and when it was the full week off, she did it without pay. If it was a day here or there, we still paid. I think she more than deserved it and we made other arrangements (or worked from home).
I asked about food policy, did she provide meals and snacks? What did I need to bring? What limitations were on me? Was a Tostino's pizza to bake in the oven okay? Was peanut butter allowed? Could he have a soda if we stopped at Subway in the morning? Things like that...
Hours! Make sure you know when they open and close, and what the late policy is.
Sick policy. What constitutes sick? Baby will get fevers with teetthing, can she give Tylenol for that with a doctor's note or no? What policy makes it so any kid can't be there and for how long....my sitter was fever free for 24 hours, same as the school system, and I understood and appreciated that.
Ask about a schedule. What will they follow? What do they do for arts and crafts? Music? Free play? Story time? Nap? Outside time? What do they do on rainy days?
Really...your questions will come as you stay there longer, and if you have a good relationship, it really should be normal conversation and not a Q&A session as time goes on.
Good luck. Definitely look now though. In MD, it can take a year or more to find a good sitter.