Wow, finally, I can brag about my home state!
We drove up to San Fran last year. We left the car at the hotel for two days and took Lyft (similar to Uber) or the BART everywhere and it saved us a ton of time. Try to catch a Giants game (baseball sucks but baseball games are super chill). May as well check out Golden Gate Bridge as it's a world-famous landmark.
On the way down, we took the 1 (Pacific Coast Highway). It took 12 hours, so be ready for a LONG drive. You will be twisting and turning along cliffs overlooking the ocean (either a thick blanket of fog or beautiful blue), punctured by random mountainous camping areas. If you do take PCH, make sure to stop at the Monterey Bay Aquarium, and if you have time for a whale-watching tour, TAKE IT! Every time I have taken a whale watching trip out of Long Beach (south of LA), I see grey whales breaching out of the water and have seen the flukes (tails) fly up in the air like they do in movies. Wear a jacket though, it is much colder out on the ocean than on the mainland.
Once you get to So-Cal, definitely do the Hollywood thing. Don't take the bus tours, those are outrageously expensive. If you're a music fan, I highly, highly, highly recommend going to Amoeba records on Sunset Blvd. There is one in San Fran (been) and one in Berkeley (never been). However, the Hollywood one is about three times the size of the San Fran one. It has three rooms on the bottom floor (Jazz/Religious/Classical/OST, Rock/Pop, and Rap/Hip Hop), and an upstairs area with movies, shows, and some books. The whole building is comparable in size to a Best Buy, so it's not just some small mom&pop record store. Still has that homely feel to it though. I have found very rare / impossible-to-find albums there, and I'm pretty sure every time I've gone to Amoeba I pick up a Radiohead EP or single that I didn't have before -- usually to the tune of $3 or less -- in the enormous Used section. There is a ton of out-of-print stuff there as you can imagine. I got both of Hum's albums there which I haven't seen anywhere else except iTunes.
Universal Studios is fun too, plus you are forced to walk through Universal City Walk to get there, which has a ton of restaurants and shops. Disneyland / California Adventure are pretty expensive these days but you may as well go while you're in town -- definitely get the park hopper as CA Adventure is finally worth going to. DL is really one of those places where you can put reality on hold for 10 hours and just enjoy yourself. Tomorrowland is the best part, and if you're even mildly interested in Star Wars, then you'll really enjoy StarTours. Buzz Lightyear Astro Blasters is like 10 feet away so try that too. In Frontier Land you can check out my favorite rides, Indiana Jones, Haunted Mansion, and Pirates of the Caribbean, complete with several animatronic Johnny Depps and a town completely up in flames with a candelabra supposedly inspired by the famously anti-Semitic Walt Disney (doubtful). If you plan on going to Disneyland, bring your own food. The food there is expensive and overrated at best.
Other random tidbits: The Inland Empire, about 40 minutes east of LA in decent* traffic (my home, the 909) is a strange (sub)urban area of like 4 million people yet it's stereotyped as hickville USA. It's basically one of those places that the LA and OC folk pass through on their way to Las Vegas. The only touristy thing out here is the Mission Inn in Riverside -- one of the old Californio missions that has been converted to a very ritzy restaurant and hotel. Everybody else has said In-N-Out and I agree with them. Any chance you're going down to San Diego? The San Diego Zoo: Safari Park (on a separate property from San Diego Zoo about 30 minutes away) has tram tours that take you very close to herds of wild animals and has other cool attractions. My favorite is the Cheetah run, where they put a piece of raw meat at the end of very long strip of land (330 feet) and you watch the Cheetah bolt toward it in about four seconds. It's over quickly but it's just so cool to watch.
Places to avoid: Mexico, unless you plan on driving WAAAY south to some of the nicer cities on the baja peninsula. The main border town is Tijuana and it sucks. You can get legit Mexican food all throughout LA or San Diego -- don't cross the border for it, as it takes like 3 hours to get back over.
Enjoy your stay!
*Be prepared to face a ton of LA gridlock traffic. But if you're with your friends and don't have a strict schedule, you'll still have a blast.