Starting from Scratch
There's no better time to start off a new lawn than the mild, showery weather of April and May. Whether you're using turf to get an instant effect, sowing seed onto bare soil, or even repairing a few worn patches in an existing lawn; the principles are all the same. First start off with a well prepared soil base, one that is weed-free, as level as you can get it and raked to a fine tilth (that's where you break up the big lumps so it resembles breadcrumbs). If you're repairing patches it's still worth raking and scratching up the soil, before mowing the grass lightly and treating it with weed killer and fertiliser.
Next lay your turf, butting the edges up to one another tightly, then scatter and smooth fine topsoil, top dressing or compost into the joins to help them knit together. Work from planks to avoid compacting the soil if you are tackling a large area, then try not to walk on the newly laid turf for several weeks.
If you're sowing seeds, prepare the ground for sowing by cultivating, levelling then firming the soil, this will allow the soil to settle before sowing later in March and April. When you're ready to sow, scatter the seeds as evenly as possible over the area, then rake in lightly and fence off to keep dogs, cats and small children away. The seed should start to germinate in about 10 days but it's usually a couple of weeks before I notice a green haze appearing. You have to allow grass a good few weeks to establish, and it will need to be 5-7.5cm (2-3in) tall before it gets a cut and then it's nothing but a light trim.