As someone who's currently shopping for some winter wheels and has the raised blood pressure to go with that, I've got a few suggestions as to what would make me pick up the phone and call your or email you if you're advertising a vehicle.
Keep in mind that if you're willing to deal with the additional hassle, you'll normally get the most money for a used car if you sell it privately. If it is worth the additional effort though is both a matter of judgement and if you're willing to put up with strange people like me :).
Depending on the value of the vehicle and its rarity/desirability, you're looking at newspaper ads (probably won't get you much of a response these days), craigslist, Autotrader and similar, and last but not least, ebay. If you're trying to sell something that's easy to find because there are five at every street corner (think beige minivan), skip ebay. If it's worth below 5k-6k, I wouldn't bother with places where you have to pay to advertise, which leaves CL for the cheap stuff - that said, I'd still stick it on CL if it's advertised in other places. Heck, it's free after all.
The figure out what sort of money you're asking for. Check the resources like KBB.com and have a look at your local CL for similar vehicles. Out here, certain types of vehicles (for example, Jeeps) sell quickly and often above even KBB.com. A little market research will help you come up with a good price. Just don't do things like asking a massively inflated price for a vehicle because you paid $x five years ago. All this shows that you have no idea what your vehicle is worth. Oh, and I'd always work out what the minimum I'd take is - leave yourself some haggle room but don't undersell the vehicle.
Once you know where you advertise and for how much, pull together the basic facts for your vehicles and the points that would make it stand out. Basic facts about the car should include engine size, type of transmission, if it's AWD (where applicable), mileage. Color I can see on the pictures, but it's nice to include that, too. If you have service records, recently replaced a big ticket item (think transmission or similar) or had a very recent service, especially a big one where you had a timing belt and waterpump changed, mention it. Don't say the vehicle has a new engine if that was put in 100k miles ago, that's nice to mention but it's not new. If nobody's ever smoked in it, mention it. If it's got other outstanding features (super low mileage, summer only use etc) make sure to mention it that, too.
Next, if it's got any faults that you know of - especially obvious ones - disclose them. People like me will most likely find the leaking shock absorber and the rust holes in the floor anyway, and it makes a much better impression if you do tell us about them beforehand. Trying to tell someone that your banana-shaped car that looks like the Blue Man Group used it for practise is actually pristine and accident-free isn't going to go down very well.
Next, pull together the paperwork - make sure you've got the title (if there is a lien on the title, check with the lienholder before advertising the car so you know their procedure for releasing the title), any maintenance records you have, manuals, receipts etc. If the vehicle has a salvage title, try to find out why and mention it in the ad. I've just had a comedian phone me while I was driving to see his vehicle and leave a message that he didn't have a title and didn't seem to be willing to bother to get one, either. Obviously that put me in the right frame of mind, given that it was a 200 mile round trip. So don't do it - if you can't get a title, the schmuck you sold it to will have even less of a chance of getting one. And given that you are in California, a lot of people (including myself) react really badly to three years' worth of back registration, missing smog, expired registrations on something I'd expect to test drive etc. Essentially anything that would stop a potential cash buyer to drive it away on the spot.
Next, clean the car - you know, the five years' of accumulated McD wrappers and inch thick layer of dirt (I'm only partially kidding, I've seem some pretty horrible stuff recently). Spend the two hours it takes to clean it or pay to have it valeted or detailed. Clean, shiny cars sell a lot better than a rolling recycling container.
Oh, and last - make the effort take some decent photos. The more the merrier, shot in daylight (no photographing a black car after sunset) and if there is any damage, an additional photo or two showing the damage would be nice. Stick the on photobucket or similar and put the links in your craigslist ad so you don't restrict yourself to the microscopic photos that you normally get on there.
As to payment, I'd either take cash, meet the buyer at his bank where he draws out a cashiers check in front of your eyes, or, well, cash. No Kauri shells, deeds on bridges in Brooklyn or anything else. Be prepared to take a deposit - a lot of buyers aren't willing to wander around with ten large ones in the back pocket to go look at a car - and spell out exactly how long the deposit is good for. I also tend to make them non-refundable (buyer doesn't pick up the car within the negotiated timeframe, you keep the deposit as 'damages' for not being able to sell it to another cash buyer).
Check your DMV's website as to what exactly you need to do once you sold the car. Here in Nevada it's the buyer's problem on how to move it as you keep the plates, but I know in California the regular plates (not personal ones IIRC) stay with the vehicle and I think you need to inform the DMV that you sold the vehicle. I'd also keep a record of who I sold a vehicle to (name, address from his drivers license, license number etc) just in case they run a few red lights and accumulate a few grands' worth of parking tickets.