Knitwear lasts a long time if you treat it gently, and falls apart quickly if you don't. Five things matter.
Wash cold, wash rarely
Hand wash in cold water, or machine wash on a wool or delicate cycle at 30°C or below. Turn the garment inside out. Use a mild detergent — nothing with bleach or optical brighteners. Between wears, air it out; most knits don't need washing as often as you'd think.
Never wring, never hang wet
Press the water out between your palms or roll the garment in a towel. Wringing distorts the stitch permanently. Hanging a wet knit stretches the shoulders out of shape for good.
Dry flat, out of the sun
Lay it flat on a towel, reshape it gently to its original dimensions, and leave it in shade. Direct sun fades colour — especially the rust, olive and navy. No tumble dryer, ever.
Fold, don't hang
Store folded on a shelf. A hanger drags the shoulders down over time.
Pilling and iron
Some pilling under the arms and along the sides is normal in the first few wears — it's friction, not a fault. Remove it with a fabric comb or a knit shaver, not by pulling. If you must iron, use a cool setting on the reverse, with a cloth between the iron and the knit. Better still, steam it.