You should store your tent in a cool, dry place where it won't be damaged, exposed to sunlight or eaten by creatures! A shed or garage is usually a great choice, but a kit wardrobe or spare room can work as well. Instead of storing the tent in its stuff sack, try to keep it in an oversized, breathable cotton bag - or a simple pillowcase can work just as well. This helps keep the fabric ventilated, and avoids any mould forming.
It’s really important that your tent is completely dry before packing it away. Storing your tent whilst it’s wet or even damp can lead to the premature breakdown of its fabric and coatings. When it comes to using it next, take your tent out of storage a day or two beforehand to give it a thorough airing and to make sure it’s still in good condition. It’s better to discover any problems before you leave, rather than out on the trail.