Although some experts recommend planting California natives in the autumn, there are an equal number of experts who feel the winter is the best planting time rather than allowing for vulnerable growth started in the last warmth of autumn to be caught by winter frosts. I've had successes and failures at both times, so I recommend trying a little of both and see what works best for your lot of land. (Of course, the deciding factor can have a lot to do with just how cold your temperatures drop in the winter.)
Some of the most glamorous perennial California natives, in my opinion, are the yellow-flowered Sulphur, Red or Conejo California Buckwheats, Wooley Blue Curls, the Matilija Poppy, Clevelandii Sage, and Carpenteria. As for showy annuals, you can plant seeds of California Poppies (sometimes lasting as short-lived perennials), Clarkia, Phaecelia, "Shooting Star" (Mentzelia), or "Tidy Tips" (Layia). The cool season is a good time to plant them on a cleanly cut (and ideally, raked) sunny hillside. Plan on losing a good percentage of California flora (and your seeds) to fauna (birds, rodents, insects, etc.) But if the rains are cooperative, you could get a hillside ablaze with California annual natives in the spring. And if they like the location, they'll self-seed themselves for years to come. Other good plants to seed on your hillside or open areas are Lupins, Galliardias, Nemophilas ("Baby blue eyes"- plant with some shade), and low native grasses. Stick to low growers wherever possible keeping fire safety in mind, especially if you live near open chaparral or undeveloped land. Larger shrubs or even trees can be safely planted on hillsides or fields if they are grouped with large clear areas in between groupings that would act as firebreaks. Keep groupings away from the house and do this only if you have a large area so you can cluster the groups in a natural design. Otherwise you will dot your hillside with plant groupings that look more like wallpaper than a flowing natural picture. If you have that much space, you can even work dry riverbeds, stairways or paths into the design creating not only a beautiful landscape, but adding more fire breaks. Remember if you are planting California natives in locations outside of California that most of them prefer excellent drainage.
California is a big state and not all natives do well everywhere. Just as you can grow many California natives outside of the state, even within California you need to choose the right kinds of plants for your climate. Coastal areas tend to get more rain than inland areas. They also have more moisture in the air and a lesser temperature range. Mountians can experience plenty of snow. Inland chaparral gets very hot and dry in the summer. And riparian California natives thrive streamside and will languish in fast-draining soil where they don't get sufficient water. In short, although most California natives are drought-tolerant, not all are and even those that have low water needs may have special temperature or humidity preferences. So, match up your California native plants with your garden conditions and you will have an eco-friendly, low maintenance garden. Most plants are quite flexible, but be careful where extremes of heat, cold and water are concerned.
Make sure new plantings get more water than nature might normally provide. And if you expect frost, throw some burlap cloth over them at night. Remember that newly planted California natives have to grow their roots out and settle into their new homes to become the tough plants they have evolved to be. A little extra TLC for the first year or two is highly recommended. Especially if you are planting California natives in the winter.