Getting Ready for 2008

I just bought a house and want to get the back yard together. I hope someone here might have some guidance. I live in Bergen County, New Jersey. I think that is zone 6.
My back yard is about 1/4 acre or so and has never really been maintained well. There is a light grass covering, but it's not really consistent and thick. Also, there is a lot of both organic debris ( from leaves and crab apples, etc) and non-organic debris including some plastic bits, some old piping, old wood slats, etc.
My first thought is to just get it cleaned up and then next to seed it. I'm not sure when. It's a fairly shady yard, but it does have some patches that get more sun.
My initial questions come down to:
1. Who do you hire for a general clean-up? 2. How do you go about getting ready for thickening the lawn in 2008.
Josh G

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