You can include vegetables and herbs in your design if using your garden as a food source is important to you. Or perhaps you want to attract butterflies and bees. Or focus on flowers for cutting or drying. Figure out what you want from your garden before you start selecting plants. Choose the hardscape features of your garden before the plants.
Good bones make good garden designs.
Incorporate a backdrop of some kind, such as a wall, wooden fence, or even a hedge. Include a path, preferably with a curve to draw the eye and welcome the garden visitor. Add a trellis or some other structure for a climbing plant or two. Rethink the way you plant. Plant in clumps, clusters, or swathes rather than in rows.