Plant daffodils 4 - 6" apart and 6" deep immediately upon receiving them. Water frequently in the spring. Cover with mulch in the winter. Peat-moss, pine needles, leaves, straw or grass cuttings are good materials to use. Daffodils are at their best in irregular plantings and random spacing. Overcrowding will reduce the bulbs naturalizing ability to reproduce more bulbs and flower each year. 

After Bloom:

After flowering, do not cut back the foliage until after it has browned naturally. Regular watering will prevent it from dying back too early. Don't over water your daffodils, though. They tend to rot in wet areas. For next year's flower production, the foliage must produce enough food to replace the strength lost in flowering. If you decide to cut the flowers, use a sharp knife and take only one or two leaves from each plant. Any more than this will weaken the bulbs. If your flowers start growing smaller and fewer, it may be time to divide and replant the bulbs. Dig up the clumps in spring and replant them right away, or if holding them until fall, place in a well-ventilated area.