The classic problem with the Bay Area coast applies here: summer is the worst season. June through August the coastal fog sits over the bay most mornings and often does not lift, with cold winds off the water and daytime highs in the mid-teens even when inland San Francisco is sweltering.
The best months are September and October, when the inland heat draws the fog offshore and the coast gets clear days, warm sun, and the Pumpkin Festival on the third weekend of October. The festival weekend is the busiest of the year in town — book accommodation months ahead, expect traffic on Highway 92, and ride a bike if you can.
Winter brings the big-wave season at Mavericks, with the best swells usually in December and January. It also brings rain and short days, but the storms can produce dramatic light and the dungeness crab boats are in full swing. Spring is a quiet, pleasant in-between with wildflowers on the bluffs and the slopes above town green from winter rains.