There's less to do at California Adventure so we usually save that for one of the days that the parks open a little later. If you go there, go straight to get a FastPass for the Cars ride and then head for the Toy Story ride. They are both great rides but get huge lines. If you don't like walking around wet, bring along the cheapo ponchos from the dollar store for the Grizzly River Run. Some people only get a little wet and others get 100% drenched to the skin (happened to me once and I'll never ride without a poncho again!).
It does help to look at some of the sites that discuss ride times and touring suggestions. I used a great book called the Unofficial Guide to Disneyland that talked about how the different types of rides affect the order in which you visit. For example, Dumbo and Peter Pan are both very slow loading rides, and they don't have FPs so if you don't get on those early in the day, you will have to wait in line for hours if you want to go on them. We usually head to Fantasyland first to ride the two I've mentioned early (and sometimes Alice in Wonderland and Mr. Toad if there are no lines), then run over to get a FP for Splash Mountain. While over there, we'll ride Indiana Jones. After that, it's a little more hit or miss depending on how the lines are looking. Some of the ones you can wait a little bit on are the Haunted House and Pirates, because they move people through fairly quickly and the lines tend to come and go. But, if there's no line when we're going by, we'll jump on it. Nemo is another one that gets crazy long lines so should probably get worked in early (although we usually just skip it all together since my kids don't love it). Anyway, it sort of depends on what you want to see (like my kids don't like Space Mountain so we never have to worry about that one), but it does pay to have a plan.
Speaking of lines. the apps that tell you wait times are awesome and can really help you decide whether it's worth running from one side of the park to the other for a particular ride at a particular time. I definitely recommend using one of those.
And back to the topic of going early, it's awesome if you are staying at a Disney Resort and can take advantage of the early park admission. To me, it's well worth the extra cost.
Oh man, you are making me want to go back!
