A courtyard, a balcony, a strip of paving behind a terrace. In the UK an awful lot of outdoor space is measured in single figures of square metres, and the usual response is to fill it with small things.
That is the mistake. Lots of small objects make a small space feel smaller, because the eye counts them all. Fewer, larger, better placed things make it feel considered.
Go up, because you cannot go out
The floor is fixed. The walls and fences are not. Vertical planting is the single biggest change available to a small garden, and it costs you no ground at all.
Wall mounted planters, a trellis with a climber, a tiered plant stand in a corner, hanging pots at staggered heights. All of it adds green without adding footprint. A climbing jasmine or clematis on a bare fence turns the boundary from the thing that closes you in into the thing you are looking at.
Use fewer, bigger pots
Fifteen small terracotta pots read as clutter. Three large ones read as a garden. Large pots also hold moisture far better, which matters enormously in a hot spell on a balcony, where small pots can dry out in a single afternoon.
If you already own a lot of small pots, group them tightly in threes or fives at different heights rather than spacing them evenly. Clusters read as one object. Scattered pots read as fifteen.
Take the boundary out of focus
Nothing announces a small garden like a bright orange fence at eye level catching the light. Painting a fence or wall a deep muted colour, a charcoal, a dark green, a soft black, does something slightly magic. The boundary recedes, planting in front of it stands out sharply, and the space reads as deeper than it is.
Pale colours do the opposite of what people expect out here. They pull the boundary towards you.
Give it one place to sit, properly
The instinct in a small space is to choose small furniture so it fits. The result is usually a bistro set nobody sits at because it is not comfortable enough to stay in.
One genuinely comfortable seat you use every day is worth more than a four seat set you use twice a summer. Work out where the sun lands at the time of day you are actually home, and put the seat there. That single decision matters more than everything else on this list.
Light it, or lose it at four in the afternoon
For a large part of the British year, your garden is dark before you finish work. Unlit, it stops existing in October and becomes a black rectangle you look at through glass.
Solar string lights along a fence, a couple of lanterns on the ground, a solar spike uplighting one plant. Low, warm and at different heights. This is the cheapest way to double the number of months your outdoor space is worth having, and it makes the room inside feel larger too, because the window stops being a mirror after dark.
Repeat one plant, deliberately
A small garden with twelve different plants looks busy. The same garden with four plants repeated three times each looks designed, and it is the same amount of greenery.
Pick one plant you like and use it several times at intervals. Your eye follows the repetition around the space, which makes the space feel like it travels further than it does.
If you do one thing
Paint the fence dark and put something climbing on it. Everything else on this list is easier once the boundary has stopped shouting.