What should I do to prepare my trenches/holes in the concrete after adding plumbing in the basement?

I had to break my concrete floor to move plumbing in the basement for a development and now I'm wondering how to prepare the trenches and holes for pouring the new concrete. There was a vapor barrier between the gravel and the concrete? Should I replace it? If so how thick was the plastic? How should I prepare the old concrete with the new I'm going to be adding? How do I get the new concrete level? Any other help would be appreciated. Thanks!