I had a small 'jungle' on a balcony less than 3m2.
- Learn the hardiness of your area. This will tell what type of vegetables you can grow.
- Check how many _direct_ sunlight hours your balcony gets every day.
- Choose the vegetables you want to plant based on the two points above (hardiness and sunlight hours). Example: if you have lots of sunlight plant full size tomatoes. If you have less than ideal sunlight exposure plant cherry tomatoes.
- Learn what you can plant in each season and when to fertilize. Liquid fertilizer is your best bet in a small apartment.
- In a balcony on a tall building, wind is the enemy.
- If you get many hours of direct sunlight (6+) and your balcony faces south you can grow almost anything there.
- Prefer a few big pots to many small ones: A few big pots means less variety but will require less maintenance, watering and the plants will be stronger because their pot is bigger. I have 70L pots and they're great. I would bother with less than 20L.
- Some fruit plants will take more than 10 years to give you fruit and others can't self-pollinate. Avoid those at least when starting out. Radish grows in less than 30 days.
- I've successfully planted and harvested Raspberries, cherry tomatoes, broccoli, peppers, strawberries, carrots, parsley, radish and basil in a small balcony that isn't even south facing in Lisbon. It never produced enough calories but it was fun and the produce was very tasting. I tried to plant cantaloupe twice but it failed mostly because of the wind (I think).
- I prefer store bought soil with added perlite and textile pots. Perliet and textile pots improve root health in small pots.