Uplight the birch (?) tree, and any other focal points, as the main value of a Brooklyn backyard is probably the view of it from the back rooms or summer evenings. You need a focal point at the farthest end - a visual and physical destination. Then you need a path to get there - again, visually as much as physically. Ponder whether you want that "path" to meander, or to lead straight to it. In either case, think about how to ENHANCE that sensation. If it's a straight path, narrow it at the end to make it seem longer. If it meanders, plan the interim objects and landscaping to create glimpses of it.Look at the surroundings and decide which features you want to capture as part of your view or which you want to screen. Make your decisions about sizes and siting of plants and objects with that in mind. I.e., an arbor may be working to block out a neighboring window (which is apt to be lit at night and thus a prominent feature in your view). Test this with something you can move around that is the eventual size of any tree or structure. In other words, first think about how you dreamed this precious open space would make life in NYC more fun, romantic, healthy, creative, peaceful, luxurious, pastoral or urbane for you. Don't neglect the practical potential of open space. For many of us urban dwellers, being able to hang up sheets in the sun is the greatest luxury on earth. I would include an aesthetic option for that. And you probably will want to entertain, work, grill out there. Don't be afraid to make that activity at the far end, serving as the destination. Now stand at that destination (whether a place to sit, stand, or turn around) and look back at your house. The view and the journey to it should be every bit as interesting. Take pictures from every possible viewpoint (windows on all floors, doorways, corners, alleys, etc.), print them, and draw on them.