We are working on developing a checklist and best practices for getting control of your lot. We will be sharing that here once it's ready. In the meantime, here are some resources that might help you get started.
Soil-building recipes from BKpermaculture.
Soil tests through Brooklyn College.
A new EPA report, Brownfields and Urban Agriculture: Interim Guidelines for Safe Gardening Practices (pdf)
Potential building materials at Build it Green! NYC.