I live in the LA area and would recommend:
- stay away from the SoCal freeways, especially between 7am-9:30am & 3pm-7:30pm (basically rush hour gridlock traffic, and if you are not familiar or feel safe with lane splitting, definitely skip it);
- if you'll be in SoCal on a Fri, Sat, or Sun, try to stop by the Rock Store in the Malibu Canyon area (it's got nice riding in the area, but be aware that it's fairly well patrolled; and a great place to see all types of bikes);
- ride up the 101 to San Luis Obispo (about 200 miles north of LA) and turn onto Highway 1
- Hearst Castle is probably 20 miles north of Morro Bay and a big tourist attraction (skip it if you've seen European castles - it's nice for the States, but not that nice in comparison; especially if you don't want to spend half a day doing this);
- continue on Highway 1 through Big Sur and on to the Carmel/Monterey area;
- follow Highway 1 up to SF, crossing the Golden Gate Bridge to Bodega Bay, Mendocino, then Fort Bragg (a turnaround point);
take the 101 south to the I5 for a quicker return trip back to LA.
I did this ride last summer and it was great! Others will probably chime in with their own recommendations. You might also take a look at one of the motorcycling maps for both southern and northern CA for other options/ideas. In any event, sounds like it should be a nice trip.