You can plant spring-blooming bulbs such as daffodils, tulips, crocus, and hyacinth when ground temperatures drop to around 50-55°F or lower (but not freezing), and continue planting up till a couple weeks before the ground freezes. If planting hyacinth bulbs, use gloves; some people develop skin irritation after handling them.
Bulbs look most natural when planted in clumps and it means digging fewer holes, so put 5-8 in a hole together, but put an inch or so of space between larger bulbs like tulips or daffodils. Most hardy spring-flowering bulbs evolved in desert or Mediterranean climates. Consequently, many (especially hybrid tulips) are not well-adapted to our wet, heavy clay soils and may only return for a few years, especially if we plant annuals needing a lot of water on top of or right next to them.
Bulbs appreciate moisture while blooming, but prefer hot, dry conditions afterwards when dormant. Bulbs need good drainage, too, so plant where the soil is suitable. If you want tulips, planting ‘species’ tulips, the shorter types with smaller flowers, may work better (or adjust expectations and treat hybrids as annuals). Species tulips include named varieties of Tulipa clusiana, Tulipa tarda, Tulipa griegii and Tulipa kaufmanni among others.
Generally, plant bulbs two to three times as deep as the bulb is tall. Large bulbs should be about 6-8 inches deep while smaller bulbs can be 3-4 inches deep. Measure planting depth from the bottom (not the top) of the bulb. Ideally, water in bulbs after planting, especially if dry. Daffodils tend to live longer in our soils than tulips, so may be a better option. If you have issues with chipmunks or squirrels digging up bulbs, planting daffodils or hyacinth, which are poisonous to them (as opposed to tulips or crocus), can deter them from digging. You can also lay chicken wire over the soil in the planted area, weighted down with rocks or bricks. Remove it promptly in spring. Another strategy is to apply an inch or so of ‘chicken grit’, available in farm and feed stores about half an inch under the top of the soil covering the bulbs. Squirrels and chipmunks don’t like digging in this material and it may discourage them but it won’t interfere with the bulbs emerging in spring.
For more general information on growing flowers, check out this website’s flowers section.