Any outdoor space can be made into a mini garden with proper planning and planting and the upside is you do not need to spend hours maintaining it. Sketching out to scale the area you have to work with is a good first step then paying a visit to a garden centre or a local open garden for inspiration should give you some idea of the effect you want to achieve.
As a general principal light colours make a space look larger so any painting of walls and fences should be in pale pastel colours. Plants should ideally be those that have pink and lilac flowers although an occasional dark coloured flower will draw the eye.
A winding path leading to different areas of the garden will create the illusion that the garden is wider than it is or alternatively a short, wide garden can be made to seem longer by the use of straight paving. Growing hazy mauve and purple plants at the end of the garden is a trick used by painters to give the illusion of distance and can be used successfully in garden planting in the same way.
A quirky idea that some gardeners use is to install a mirror in the garden that is angled to reflect some of the plants. A mirror can also be used to reflect light to more shady areas of the plot.