I went to SF a couple of times in the 1980s and we had a couple of days stopover in LA a year or so ago. We had a car in SF and ten days so we did about 1800 miles and I can recommend:
Yosemite - an absolute must. If you do nothing ekse, do this. http://www.nps.gov/yose/index.htm
Muir Woods giant redwoods are interesting. http://www.nps.gov/muwo/index.htm
Sonoma valley and Napa Valley. I was recommendeded the Simi winery http://www.simiwinery.com/
Monterey, Carmel, Pebble Beach and the 17-Mile Drive are beautiful. http://www.pebblebeach.com/activities/explore-the-monterey-peninsula/17-mile-drive
The giant sequoias are worth seeing, there are a couple of groves. http://www.fs.usda.gov/sequoia/
I wanted to go to Bodie but didn't have time http://www.bodie.com/
In SF the Bay Cruise and Alcatraz
Columbia Gold rush Town http://www.visitcolumbiacalifornia.com/
In one day we drove SF - Modesto - Yosemite - Carson City - Reno - Sacramento - SF but our stops were limited by a slow puncture just inside Nevada. The 10-day visit was in March and the weather was like an English summer, all sunshine and green grass. I went back in June and all the grass was parched and it was much drier.
In LA all we had time for was a one-day city tour doing Venice Beach, Downtown, Old Los Angeles, Sunset Boulevard and the homes of the famous.
Do your research and you'll have a great time. California is a lovely place and I would love to go back for longer.
Have fun!