Start laying your lawn along a straight edge, butting the ends closely together. On subsequent rows, stagger the joints like brickwork, ensuring there are no gaps. If you need to adjust the position of the turf after unrolling, always push it rather than pulling it to avoid stretching. Work from planks laid on the soil to avoid making footprints.
Make sure that there is complete contact between the underside of the lawn and the topsoil. If necessary, tamp or roll your lawn lightly as you go along. Try not to leave any gaps between the turf, if they do occur they can be filled with topsoil and lightly firmed.