The latest recommendation is that you don't. Instead, cover the soil with a 5-10 cm deep layer of organic mulch, with the lowest couple of cms a rich, fine textured compost, and renew that twice a year. The immediate effects are to slow evaporation from the soil surface, reduce wind erosion, and even out fluctuations in soil temperature. Soon after the mulch is applied, soil organisms--such as earthworms--multiply and start turning in the compost, while decay products filter down with rainfall and watering. In a year or two, depending on temperatures, about 15 cm of good topsoil will have formed. After 5 years, about 30 cm of topsoil will have formed, the subsoil will gradually be improving, and sensitive plants such as Japanese Maples and Magnolias can be planted. In flowerbeds, compost can be incorporated into the soil for quick effects, but likely will mostly vanish before the end of summer, due to the rapid bacterial action in sandy soils. Whatever method you use, a slow release form of nitrogen will help reduce the nitrogen debt caused by those bacteria.