Make a plan
Start by making a scaled plan of the space indicating all the pipes, utilities and passages. Keep in mind that the smaller your garden is the higher you will have to go. It's important for you to draw all of your ideas to get a general picture of your vision, but mostly you need to stay realistic towards your needs, a packed garden is not relaxing.
Clear the centre of the space
Keep the centre of the garden free to give the impression that the space is bigger than it actually is. If your garden is longer that wider then don't plant along the sides to avoid the corridor feeling. If the space is wider than longer then, this time, plant along the walls to give the impression of depth and so making your garden feel longer that it really is.
Very in right now, Japanese gardens are a perfect model for small spaces. The art of gardening is very important in Japan. For the Japanese, gardening is the interpretation and idealisation of nature with limited devices. To keep with the style you need to incorporate water, wood and rock elements.
There's a dry variant of these garden, the Zen garden. The objective is the same but you need to replace the water elements with sand or gravel. If you want your garden to be pleasant and useful, why not turn it into a mini vegetable garden. There's no need to fill the space up, a few vegetable varieties should suffice. In this case symmetry is no longer important just go with your gut.
For small gardens climbing plants are ideal to add colour to your garden without clogging it. Smaller gardens are more present in big cities so gardeners have had to adapt their product to the demand. The result: There are, now, miniature versions of your favourite plants.
Before starting to plant you need to test your soil to determine the level of pH because some plants can't survive if the level is too high. There are little things you can do to make your garden feel bigger: make sure you vary the height of the plants, do not break up the space and of course, use different shapes and soft colours.
With this information you can get started, without forgetting the most important thing: this is your space so have fun with it. Let your imagination and creativity roam free so that the garden reflects your personality. Lara Ronayne Casimiro