Decrease the frequency of mowing and gradually increase the height of the cut.  Worm casts may become a problem at this time of year: disperse them when they are dry, with a besom broom or an up-turned wire rake moved from side to side. Earthworms are less abundant in acidic soils, and the regular addition of spring/summer lawn fertilisers based on ammonium sulphate may make the topsoil acidic enough to discourage earthworms. This is a great month to scarify the lawn and follow it up with spiking to aerate the soil below the lawn. Feed the lawn with an application of autumn lawn feed. Re-seeding or re-turfing is best done early in the autumn as the ground is still warm from the summer but is also moist. For the last cut of the year, simply 'top' the grass.  Regularly brush up autumn leaves.