There are a number of things to consider when planning your next landscape bed or shrub border, like whether your plants need sun or shade, whether it flowers and what color, how large it gets, and so on. Another important trait to consider is the plants foliage and characteristic, and how it looks next to the plant beside it.
Using two plants with foliage of different size, shape, and color will add contrast and visual interest to your landscape. You could try a combination like Dwarf Gingko and Golden Spirea to create a nice contrast. Avoid using plants that are too similar next to each other, like Green Velvet Boxwood and Soft Touch Japanese Holly. Each is a nice, beautiful plant, but together there isn't much contrast.
You could also try a striking contrast like a big leaf Hydrangea in green and the thin-foliaged maroon leaf of the Japanese Maple. Or even a Conifer coupled with the broad leaf of a variegated Dogwood. Color, texture, and size contrast will all help to make your landscape more visually interesting.