I was a professional nanny for twenty years and a mother. I know how hard it can be to leave your children in the care of good hands.
First, I would ask around friends, family and neighbors.
Second, if you go to a church ask the youth group leader
Third, try posting at local colleges
Fourth I would try care.com
I would interview the person at your house, just ask questions you want to know. Make sure she/he '"feels" right to you. Then have her/him play/interact with your children. It's okay for you to be in the house while they are there.
If you want the same person you need to be good to them. Make sure that you can give them dates ahead of time so they can plan out their nights/weekend. Always thank them for a wonderful job. Leave great instructions, like if sad favorite toy is ....., what tv or movie could they watch if needed, what is there favorite book. just make sure that the instruction are no longer on one page. Make sure that the person that comes over is only babysitting, don't leave toys out for them to pick up later, and bathe your children the night before or early that day. If they need to feed the kids dinner make sure you have food either order(and for her too), or several choices for her to choose from at home.
One thing I found out when you need a great sitter if you treat them great, they will always want to sit for you. That doesn't mean you need to pay them way over the top, just thank them and treat them like you would want to be treated.