Daylilies prefer full sun. They will do respectably in light dappled shade.
Occasionally, foliage is damaged by hard late spring frosts. It is worst on evergreen types and varieties that emerge especially early. Foliage can be blemished by slugs or insects, too. For whatever reason, whenever daylily foliage is less than desirable, it can be refreshed by cutting back almost anytime except for fall. Using clippers, shears or a very high set mower, chop the plant tops back to 4-6". You won't harm them and within a couple weeks they will re-grow and look great.
The most frequent question we get is "What is the scape?" The scape is the stalk that bears the buds that open to flower. The life of the scape is only viable while it holds active flower buds. Once the buds are spend, the scape begins to die. Cutting them out is optional. You cannot largely hurt or help the plant by cutting out old scapes. It does improve a plant's appearance when dead scapes are removed. In many cases, they don't even have to be cut: once they have turned brown give a light tug and they will pop right out.
Like all perennials, daylilies eventually need refreshing through division. Once they become crowded, their bloom performance (especially the repeater-types) can fall off. How often this occurs is determined by many factors such as: variety differences, soil quality, nutrient and water management, site placement and other things. The general timing need for dividing varies from three to seven years. If bloom production seems reduced from overcrowding, dig and divide them.
For each major clump, dig it up, cut it in quarters, then replant the chunks allowing some growing room around each one. 1-2' makes a good spacing. The dividing can be very crude and performed with a sharp shovel or old hand saw. If you end up with too many plants, spread them to other parts of the garden or give the gift of gardening to you friends, family and neighbors. This dividing can be done almost any time of the year but the ideal seasons are early spring and early fall. Don't be afraid to cut the foliage back almost to the ground when you do this: it won't harm them a bit.