Graph paper is excellent for this purpose. On graph paper you can outline to scale the shape and size of the flower border, and the placement of plants within this border. Plants should be arranged so that the short ones are in the front and tall ones in the back. Let's take up the first consideration, relating to your objectives. You might be interested in the display of certain floral colors or a variety of colors throughout the growing season, or you might prefer different forms, colors, and textures of foliage.
Some gardeners prefer fragrant plants.
In general, a larger garden offers greater flexibility in the choice of plants to achieve various garden effects. To select plants for special purposes you need to consult garden books for lists of plants classified according to use such as edging plants, background plants, rock garden plants, plants for dry areas, plants for wet areas, plants for sunny areas, or plants for the shade. Some of that information is contained in this Yearbook. The second consideration deals with limitations imposed by the environment. Prevailing winter temperatures determine to a great extent the type of plants that can be grown.