In the previous post "How to get to Machu Picchu", I mentioned about the few ways on how to get to the ruins. You can go straight from Cusco, or you can go to Ollantaytambo first, stay there overnight, and then take the morning train to Aguas Calientes. Many people recommend this stay in Ollantaytambo, because in Aguas Calientes (start point to Machu Picchu), there is not much too see, it is built mainly to accommodate and serve tourists.
However, if you have only one day to visit the Machu Picchu site, I would say it is better for you to be in Aguas Calientes the night before. This is because you really have to wake up and start climbing as early as possible, and if you decide to visit Wayna (or Huayna) Picchu and Machu Picchu Mountain, you will need a lot of time for this.