There are always your typical string lights to choose from, but if you want something unique, you could go for curtain lights, stars, or globes, even add some candles!
Choosing your plants for the Christmas season is rather simple. Fir trees are the most obvious decision. Don't have the space for that? Why not some poinsettias?
A garland might be the first thing people think of when decorating a balcony. It's so simple to drape or wrap around the railing!
Think about how you can use your current décor theme for Christmas. For example, a Scandi arrangement would use lots of wood and neutrals, whereas boho would include lots of texture and oranamentals.
These apartment balcony Christmas decorating ideas should provide some guidance for how to effectively use your space. Take some inspiration from this and make it your own!