If you have a little bit of time, I would skim read
HydroGuy's DLR Guide for WDW Vets. For the most part, it'll help you get a sense of
Disneyland and some of the similarities and differences with WDW.
First question: do you have park hoppers? The two parks are very close together (about 110 yards or less than half the distance from the flag pole to the Partners Statue on Main Street). Park hopping is very easy and quick, but some folks prefer to focus one park. Personally, if you have the funds, I would get the park hopper and experience both DL and DCA. Otherwise, I would probably focus on DL even though DCA has Carsland (which is my favorite part of DCA).
DCA will be having Extra Magic Hour (EMH) tomorrow, which means TSMM and RSR will already have a line by the time the park opens to the general public. I would get a FP for RSR and skip TSMM (because it's pretty much the same as at DHS). The parks are operating on Spring Break-season schedule, which means long operating hours (e.g., 8 to midnight for DL and 8 to 10 pm for DCA).