The idea is to keep at least 10% of your lawn uncut through summer, letting a variety of native plant species grow through. These 'weeds' are the food plants for a variety of caterpillar species, and therefore as well as increasing the number of moths and butterflies that will emerge, also provide a vital source of food for small birds.
You can put up a Blue Heart preferably made from recycled materials to show that this area is being deliberately left for wild life.
A lawn as a mono culture is one of the most difficult things to maintain with out using chemicals. Chemicals that will get into our ground water and eventually effect wild life and humans. Use a pointed knife to weed out ragwort and unwanted weeds, rake out moss, but try leaving an area uncut and you will be surprised by what will grow.
Many of the open gardens this year had already created ares of uncut grass which were teeming with wild flowers and wild life.
Cut and rake the long grass in September.
Keep a corner of your garden completely undisturbed at all times, letting native flora such as bramble or hawthorn provide impenetrateable cover for small birds and snails.
Do not use slug pellets. They kill snails and go up through the food chain to kill hedgehogs.
Keep any 'garden waste', as this makes perfect wildlife habitat and should not be removed. Heap up the hedge clippings from an Autumn cut and put leaves on top. This is ideal habitat for hedgehogs and costs nothing.