Let's for now, assume that You know absolutely nothing about the subject. You have a virgin area, or an existing lawn to develop. There are several things to be considered. First, are you certain that the area contains no underground irrigation pipes, phone lines, cable TV wires, large tree roots etc.
Most perennials prefer good levels of sunlight, about six hours is optimal.
If you are planning a shade garden, two to four hours is the target range, with morning or evening light being preferred. If water supplies are restricted, choose appropriate plant material by consulting your grower or supplier. You should have unrestricted access to view the area from the location of your choice, say a living room window, an approach pathway, or a garden bench. If not, find out and make the required modifications. This will determine where in the planting you will position individual plants.