I'd price them at whatever you're happy to accept-be expected to haggle.
Make sure everything is cleaned/ironed so it looks in the best condition possible.
Make sure any toys and equipment is as clean as possible.
Bright coloured tablecloth if possible-a length of fabric from a haberdashery is fine.
Take change with you and plastic bags.
Be approachable and say hello/weather talk to any prospective customers.
Encourage picking up of items to look at.
If you can get a rail for any clothes I'd use a rail.
Cardboard boxes for books/very small toys or sets of things. So a box of books for example-write the price on the box. A collection of a play set/garage/train track all in a small box each.
Put the tall things at the back of the table and the smaller at the front.