If the soil is poor and is basically subsoil, and clay then if it were me i would clear most of this subsoil out and buy some decent topsoil, level it, then heal it in, do this a few times, raking it level each time, then leave for a week to settle, in doing so if any hollows appear you can rake them level, far better to get the preparation right before turfing, and remember to keep the new turf watered in for aprox 2/3 weeks so that it can knit together, julien.

I agree topsoil would be best spread on top if you know some one with a roller that they can lend you it would be best to use one of those to get a level lawn or get the kids to run over it up and down or as above like Julien says heal it in, when you have it level just scry with the rake and then cast seed if you are doing seed then lightly rake over the seed, you will need box s of seeds which will tell you one the box how much area it will cover and string to deter birds, crossing it closely like diamond shapes about 3 or 4 inch off the ground and some sticks to peg and tie around the string and a rake as Julien says, and water with a gentle rose so not to disturb the seed, I have done many lawns I have moved 30 times and always found seed has less weeds than turf as you have to lay turf the right way too.