I am dealing with exactly this problem and, like you, it is driving me mad. So, I will await answers to this question with interest!

It's not difficult, just a fussy, time consuming job. Spread the soil over the area - now walk all over it with your heels, every bit of it, to squash it down. Now rake it up, filling in the soft spots, moving the soil around to do so, or adding more where necessary, to get a level which allows room for turfs to sit on top. Now walk over it again. If there are no more soft spots, rake over lightly, then tamp it down with the rake with the shaft held vertically and the head flat on the ground. If you're satisfied its now reasonably flat, throw Growmore all over it, so its like fallen blossom, and then lay your turf.
One other thing - if the depth of soil you have added is more than 2 or 3 inches, its probably better to prepare the area as suggested, then wait a week for it to settle down - and then see where the level is, it may drop yet again as the soil settles back.

Thank you, kind sir, lol;-))

thanks for the advice there was a load of soil on which we did the soil shuffle up and down a couple of times. the rains helping it settle too and making the holes stand out, will rake and spread again when its dry enough :)

I like that, the 'soil shuffle', ha ha - although actually, its much more a stamp or digging your heels in...

The soil shuffle is great exercise for your legs, so even though the soils not level I have now been signed up bu the local footie team lol

This is where I wish I had bigger feet!

You only need bigger heels ojibway, and I don't mean stilettos...

:o) No, they're for spiking the lawn.

;-)

Or killing slugs?

Oh, yuk - if the heels are really spikey, the slugs would be squished onto them and have to be cleaned off...

Bamboo's answer is spot on, but you mentioned that you wanted it LEVEL.
For this you need a straightedge, as long as the area you're going to lay the turves. And a spirit level, preferably a long one, to place on top of the straightedge. As you do the "heel dance", keep trying the straightedge lengthwise, across and diagonally.