Since it doesn't seem to be a normal earthquake I wouldn't worry too much about after shocks - little quakes that happen once the main quake is over.
But we do live in California so it's probably better to be prepared no matter what. As soon as you feel the shaking, get under a solid surface. The kitchen table is a good one. If you can get to it quickly, something to cover your head and neck is a good thing to have, too. Same goes for if you're out in a store. If you're outside, just try to get into an open area away from anything that might fall.
They can be very scary and they're dangerous if they're big enough, but you can absolutely make it through one with just a little extra bravery.