Deciding on exactly what you want to use your balcony for is the first step in transforming it. You might want to create the perfect sun trap, a relaxing reading nook, or an alternative dining area. Given the inherently small nature of most balconies, it's unlikely you'll be able to do more than one of these things, so it's important to know exactly what your priority is from the outset.
What's your core aim? Are you looking for a space in which to entertain guests, an extension of an indoor space, somewhere to put your feet up and forget about the world, or a haven of green packed with beautiful plants?
Before you do anything, carefully measure your space and plan what you intend to do with it. Creating a firm plan before you start will enable you to be as efficient as possible in your use of space. It will also give you a chance to consider whether you want
bespoke furniture or
handmade furniture, that has been specially crafted to fit your balcony and save space, like a folding table clipped to your railing, or attached to the wall.