Summarize this article:

Daffodils grow best in full sunlight, however, partial or light shade is also acceptable. Full shade will keep your daffodils from blooming for the first year or two after planting. Daffodils should be planted in the fall, preferably in October. However, you can plant as early as September or as late as November. If you live in colder climates, aim to start your planting 2 to 4 weeks before the ground freezes. Buy your bulbs from a reputable source or nursery, and plant them within a week of purchasing. The larger the bulb, the better. Do not buy bargain bulbs, as they might not have a flower in them. Never buy or plant a soft daffodil bulb, as that means there is rot or another disease inside the bulb. Bulbs with two tips will produce two stems. Small bulbs may not flower in their first year.

Summary:
Pick a site with full sun. Plant the daffodils in the fall. Buy the bulbs when you're ready to plant.