Plan for the Future
You need to imagine your back yard in a few years when your landscape has filled in. It is bright and sunny now, but what will it be like in a few years? Think about your deck, the tree and shrub growth, and buildings, pergola, and any other items in your landscape that can change with time causing shady areas. You have to think about which plants need more sun and which need shade.
You need to make sure your layout incorporates the growth patterns of your desired landscape to insure all plants will stay healthy. You can move some plants later if you must but your beginning basic layout should incorporate the changing growth and shade patterns for optimal overall landscape health.