These increase by seeding and they do increase over time, both in clump size and in new clumps, often some distance from the original. Like most of these spring bulbs, full sun to light shade is preferred. The location is important because the foliage needs to continue to grow after the flowers are done in order to store enough food for next year's blooms. This is why a shady location doesn't work as well and will result in decreases in flowering both in size and quantity over time. Most of the spring bulbs have foliage that is pretty unobtrusive and can be left as is until it dies back naturally which will happen as soon as it starts to get hot. You should never cut back the foliage. Daffodil foliage is sometimes braided to keep it neat. This works really well if you only have a dozen daffodils, but we have many thousands of them spread all over the 10 acres of gardens (plus some that have seeded in the edges of the woods) and it would be impossible to neaten them that way. As the daffodil foliage starts to get unkemp, we simply flatten it to the ground and kind of gather it together - easier to do than to write - so that it doesn't cover its newly emerging neighbors. Here that would be mostly daylilies and peonies.
This last picture is marked as a Chiondoxa, and the flowers look right though the foliage seems a little wide. There are a number of different cultivars, so I'll just say it really is a Chiondoxa, and if not, its still a pretty spring flower.
Jane - where spring is really coming even though it is 3 degrees farenheit here this morning.