Well I live in Hawaii and have flown several times back and forth between the mainland. While I have had many smooth flights, it is also very very common (and completely normal) to encounter some air turbulance halfway between cali and hawaii. I don't mean to make you worry, just go into the flight expecting some very mild turbulence that both the pilots and planes are very equipped to handle. If you drink alcohol, a nice buzz tends to negate any fear turbulence may cause.
If, while you are here, you fly to maui, you can definately expect a bouncy ride into the airport there mainly due to the wind coming through the center of the "valley isle" where the airport is located.
Don't worry. Remember, at any given minute there are about 1 million people in the air so this should give you some confidence in the success rate of air travel.
Enjoy the trip! Its been a little windy and rainy here but hopefully things clear up for your stay.