For
Disneyland I would get your FPs in this order:
Space Mountain
Indiana Jones
Splash Mountain
Matterhorn
Star Tours
Honestly the only rides you "need" FP for are Space and Indy and Matterhorn (maybe, haven't tried it since they opened). Splash, Haunted mansion, Astro Blasters, Big Thunder, Roger Rabbit, can all be ridden standby in the mornings with a minimal wait! If you want to ride Splash in the heat of the day though, FP is good for that since the line will shoot up from 10 mins to 60 mins when it gets hot.
In DCA FPs should go in this order:
Radiator Springs Racers
World of Color (this can be gotten at any time - it is "disconnected" from the others)
Soarin
Toy Story Midway Mania
Grizzly River Run
Goofy's Sky School
Again here, you don't really "need" FP for Goofy's Sky School, and Grizzly is the same as Splash where it can be ridden morning or evening fairly easily, but in the heat of the day you'll need FP. You definitely don't need FP for screamin, that line moves very very fast. But the FP is still convenient as the return time is never too far off.
The most important tip I can give you is be flexible, and be aware of when you can get a new Fastpass! Also, the Disneyland app will show the current FP return time, so I always check that to be sure the return time will fit into my plans before I head over to the kiosk! Also, get Park Hoppers! But be aware that you cannot hold FP in both parks at once (the systems are "connected", but you can get a FP in either park once your new window opens)