Well, welcome to the DIS and enjoy
Disneyland! As a frequent WDW visitor you may find Disneyland to be like a "bizarro world" where theings are quite similar, and yet not the same. For example, Big Thunder Mountain is on the "wrong" side of the rivers! Study a map, ha ha.
With a single day you will never be able to fit everything in. DLR actually has the same number of attractions in two parks that WDW has in four! I recommend focusing on the things that are in DL that WDW doesn't have. DL still has many of the classic dark rides in Fantasyland. However, just because something has the same name doesn't mean it's the same. Space Mountain is totally different inside, and Pirates of the Caribbean is much longer with more scenes. Some things are quite similar though, like Haunted Mansion, Peter Pan, and Splash Mountain (though it's a little different - they all are). If you like comparing and contrasting, then you may want to make time for them.
Don't discount California Adventure though! There are some great rides here. Do check out Radiator Springs Racers, though lines are long (use Single Rider if you prefer - there are a lot more Single Rider attractions at DL and they can save you time). The new Guardians of the Galaxy version of Tower of Terror is very popular as well, and I hear it's cool. The nice thing is you can walk between the parks, so I usually treat the whole complex as one big park.
Have fun!
Dis-Friend --- 
To Disney
