The main rule – the leaves should not be exposed to light, moisture, and (preferably) alien odours. The best is to use either an opaque bag, preferably a vacuum one, or a ceramic tea box. Tin cans can sometimes suppress the aroma, and paper bags allow moisture in.
Green, white, yellow, and almost all of oolong teas (except Guangdong ones) are best stored refrigerated at a temperature of about +5°C. But if you have an open (non-vacuum) bag, it would be better to put into a cupboard than a fridge with other food in it. Tea absorbs odours very quickly, and even a few minutes beside some cheese, meat or something else will have it smelling just that.
Red, black and Guangdong oolong teas don’t really need to be stored in a cool place as long as it’s dry and light.
How long to store?
There are some points to keep in mind: young leaves and buds plucked in the spring and made into unfermented varieties are ideally consumed in the next three to four months, oolong teas can be had year-round, and fermented teas give warmth during cold seasons. This method of consumption allows us to get all the vitamins, minerals, and amino acids from the tea leaf, but, of course, should you wish to quench your thirst in the winter, a cup of green brew will do perfectly fine.
If stored properly, high-quality oolong tea leaves keep their aroma and taste even 5 years after the package has been opened.