Tea's flavor is easily tainted. Store it in a dark, airtight container with no risk of dampness and away from spices and strong-smelling foods. (Glass jars are okay as long as you keep them inside a cabinet.)
If you buy in bulk, keep most of the tea in a large container and use a smaller one for everyday use to limit air contact with the tea leaves. And keep that small container of tea as full as possible to eliminate air space.
If you reuse the tins, be sure to let them air out completely before refilling with a different tea.