I also visited Universal Orlando recently and had only one day to do the parks.
I started in Islands of Adventure and did Cat in the Hat, Caro-Seuss-El and One Fish, Two Fish. Then I walked through The Lost Continent and into The Wizarding World. Forbidden Journey was a walk-on, as was Dragon Challenge. Then I did Jurassic Park River Adventure, ate lunch in Toon Lagoon then proceeded to Marvel Super-Hero Island and did Spider-Man (single-rider), Hulk twice (single-rider) and Storm Force Accelatron. I was done with Islands of Adventure by 1:00.
Then, I walked to Universal Studios and did Shrek-4D, RockIt and Mummy. I then walked to World Expo and knocked out The Simpsons Ride and Men in Black: Alien Attack. After that I ate dinner at Lombard's and finished Universal Studios at around 6:30. I concluded the night with Islands of Adventure again, but I'm sure you don't need to do that. We did not do Despicable Me because the wait was about an hour.
I think you can do the parks easily if you...
- Get there at opening.
- Skip full-service meals (We ate at Lombard's, but you could use the time it would take to eat at a full-service restaurant to queue for Despicable Me)
- Utilize single rider. The waits that day were short, but with single-rider, we were able to walk on most attractions.
- Start with Islands of Adventure and go counter-clockwise to get to The Wizarding World first. Then do the rest of the park.
I hope you at least have a full day, because you'll need it!