You are correct that ammonium thiocyanate is hygroscopic and deliquescent, which means that it absorbs water from the air and dissolves in the water to become a liquid. We recommend that your school store your new bottle in a desiccator, ensuring that no incompatible chemicals are stored in the desiccator along with it.
Hygroscopic solids can be protected from moisture in the air by storage in a desiccator along with a desiccant. There is quite a range of substances which can be used as desiccants, however, taking into consideration safety, availability and ease of handling, we recommend silica gel. Silica gel is available as self-indicating, which means that it will change colour with the absorption of water. Silica gel can also be regenerated by drying in an oven at 105–120° C for 2–3 hours.
It is also important to protect ammonium thiocyanate against the light, as you are aware. It usually comes in a light-resistant container and your chemical store should not have direct sunlight entering, both of which would minimise the exposure to light.
We have previously answered a related question see:
'Ammonium thiocyanate', Safety Data Sheet, Chem-Supply website, https://www.chemsupply.com.au/documents/AA0101CH17.pdf (February 2014)