My first visit to Universal was a one-day visit with my family with a focus on HP as well (although before Hagrid's opened). Before we went, we decided on which rides were our priority, which were second-tier, and which ones we wouldn't mind skipping if we didn't have time.
We started on the Universal Studios side and caught a couple of the big-name rides first at rope drop to try to beat the crowd (I think we went to Rip Ride Rocket first and then Mummy), and then we headed in for the HP sections. We started in Diagon Alley - Gringotts, Ollivander's, and general sight-seeing there, and then we headed for the train to go to Hogwarts. I liked the idea of experiencing all the Harry Potter stuff "in order" based on where Harry went first in the first book.
After exploring Hogsmeade and doing the Journey to Hogwarts ride (and then recovering from the resultant nausea because that ride is really bad for my sister's and my motion sickness, although it has improved slightly since then with the clearer video upgrade), we then went for the rest of IoA. Hulk was closed at the time and Kong hadn't been built yet, but I think we did Posiedon (again, that was partly to give stomachs time to recover), Spiderman, and Jurassic Park. And then at that point we had our priority list out of the way and we sat down for a bit to plan out which of our second-tier preferences we wanted based on the time we had left.