Start with the large-scale features that outline the context of the situation before zooming in and working on the nitty-gritty. When designing water features, for example, begin by looking at the topography of the land. How do the slope and the contours direct the water when it rains? Where does water pool? What areas stay dry? Where does the sun shine bright all day, and were is there perpetual shade? How and when do people walk around this landscape, and which direction do they come from? Questions like these will help you see the patterns that exists within the system that are hard to change. Once you see these patterns, the details of what design elements should go where will become apparent.
Check out this post on the concept.