If you are only spending one day in the parks- do
Disneyland.
Assuming your teens like the more roller coaster style rides, I would:
RD and head for Space Mountain, then Star Tours, then ride Matterhorn, and make your way over to ride BTMRR.
Keep going around that side of the park, and grab a fast pass for Indy or Splash, depending on the return or wait time for each.
Then hit the classics- POTC, Haunted Mansion, and Jungle Cruise.
Save Fantasy Land for later at night- if you go after fireworks, it should be pretty close to empty.
August will be pretty hot- especially afternoon. That's a good time to check out the Tiki Room, or relax in Moments with Mr. Lincoln if you just want to sit down.
Hungry Bear is one of the best summer lunch spots, IMHO. It has a lot of shade, and the most seating. Food is pretty good, and it is in a good spot to just relax.
Most of all- get there early early. You can get way more done in that first hour and a half than you will accomplish in the whole rest of the day.
I'm sure others have suggestions, but that's how we do our days. Just DH and I , so it's two "adults".