Put some fertiliser on the soil before laying it; this will encourage the roots to go down to bond with the soil.
Remove any weeds (including roots) before laying soil, otherwise they'll just grow back through it.
Make sure soil is flat before laying it, otherwise it'll look lumpy. If this happens, you can level it out by spreading a thin, levelling layer of sand on the lawn - the grass will grow through the sand, and when you go to mow it again, a new level surface will be formed by the sand.
Make sure the edges knit together properly; you don't want the lines where the rolls meet to be visible.
If possible, don't walk on it, and keep animals off it for a few days afterwards.
If you can't lay it all in one day, roll it out somewhere temporary and water it. If you leave it rolled up, it'll die.