Important things to think about:
schedule - how many hours per week will you need a nanny? 30 hours? 40? 50? Many (if not most) full time employers guarantee a nanny's pay.
Think about it in this situation: You have the nanny scheduled from 8am-5pm, Mon-Fri (45 hours/week). One day, you decide to come home early. You let the nanny go home. If you're guaranteeing pay, the nanny will still get paid until 5pm, even though she got to go home early.
Do you want a nanny all to yourself, or do you want to participate in a nanny share?
Pay will depend on how many children, location, and how many hours you need a nanny.
When interviewing, I think it's better to find nannies nearby. If your nanny has a long commute, you could run into issues with traffic delays, inclement weather delays, etc.
Will either parent be working from home?
Do you have any pets?
Do you want a nanny who drives (while it might not seem important in the beginning, think about later on down the road if you want a long term nanny. Parks, playgrounds, libraries, etc)?
I'll try to remember to come back with more suggestions. Good luck, OP!