Many people are asking this same question, so here are a few thoughts to maybe give you a start.
For great garden decor use your imagination in growing plants in pots or a planter made in the shape to suit the area out of wood for example.
This in itself could be a feature if you make it yourself out of rustic timber using the wood from a pallet which can be bought cheaply or sometimes free, a split log, or let your imagination run away and take a walk through the bush and find straight branches to make the outside, on a square or oblong frame which you have prepared beforehand (as they say on cooking shows) or make the four corners from sturdy logs, and go from there.
The inside you could cover with thick plastic, fill with soil and plant straight in, but of course there is no drainage so do not over water on this one or else put your pots inside the planter.
Here you can use the plastic pots as they are not on display, your call whether you use saucers underneath.
This could create a wonderful sight if filled with the same flower, either the same color or varied, especially if it is a variety that will hang over the sides, but to create that voomp it needs to be full.
If that isn't what you are about then a cluster of pots look great. Before you begin have a think what you want to create, ie do you have a color in mind for plants? same color pots? same size or various sizes in the same shape and color? or a few colors that compliment each other. Try not to let it just be a haphazard mishmash.
If there is a lot of sunlight on the balcony the pots will need watering most days, so choose reasonable sized containers and have a saucer underneath and try not to dribble over the saucer as it will stain the balcony. There are little feet you can purchase to keep the pot elevated to stop this if it will be a problem with the pot constantly sitting in one place.
Hanging baskets can be another answer to having pretty flowers or edible food, such as strawberries, or herbs growing on the balcony, but here you will have water running out of the baskets and they need watering more often than pots.
Wall planters or a vertical garden, or even planter bags for potatoes are other garden accessories that are available and affordable. Planting in the pockets of any or all of the above mentioned,with herbs, veges or flowers all growing together could look fabulous and a great thing with is that you can take everything with you if you are renting and need to move on.
If you are new to planting, ask at the nursery what type of plants would be suitable for your needs, but just start and have fun. We all have plants that sometimes just die but try again and keep them watered.
I have attached a few photos, some ideas could be altered to suit a balcony, but thought they were just great ideas to include.