How you store your bag between trips affects its lifespan. When you arrive home from a trip, first air out the bag inside-out for a couple days to make sure it’s dry. Then store in a large mesh/cotton storage sack—often included when you purchase a sleeping bag, but also available separately.
Do not store your bag compressed in its stuff sack as this will eventually damage the fill. Watertight storage bags are also a bad idea. Condensation can build up inside them and result in mildew. In short, allow your bag come to its full loft with plenty of cool, dry ventilation.