Use the weather to your advantage: Observe the location of standing puddles left by winter rains; note where you need to improve drainage for plants.
Finish pruning fruit trees, vines, and bushes.
Sow seeds of geraniums, peppers, tomatoes, and eggplant in pots filled with a peat moss/vermiculite mixture; set the pots on a sunny windowsill or beneath lights until it's warm enough to plant them outside.
In the garden, "scratch in" wildflower seed mixes and California poppy seeds; plant nasturtium seeds a bit deeper.
Set out transplants of pansies, calendulas, and primroses.
As the soil warms, plant carrots, broccoli, lettuce, spinach, cilantro, parsley, and Asian greens.