Thank you for all the helpful info! I wish we had more than a day to conquer it all
I'd say start with Gringotts at park opening, then take the train over the Hogsmeade, ride Forbidden Journey then head to do Jurassic Park and explore that area - there's more than just a ride, it really is wonderfully themed, and if crowds are light head over to do Spider-Man, and you'll have had a good taste of the non-Potter side of IoA.
Then head back to Hogsmeade, enjoy the other Potter attractions (Dragon Challenge, Hippogriff), lines won't be too long, and explore the shops. Don't bother with the Ollivanders wand thing, it's not very exciting, the line is long, and they do an identical show with a much shorter line over in the Diagon Alley branch if that is of interest.
When done with Hogsmeade, maybe do another single rider to walk-on to Forbidden Journey (the single rider line is quite hidden but just ask if you're not sure) get the train over to Diagon Alley and enjoy the shops, shows and wizardry... if time, and if the line is open, maybe do another single rider of Gringotts.
Don't miss Knockturn Alley - it's quite hidden, but is quite spectacular, you can easily spend a good half hour exploring that.
Once Pottered out, get a taste of the rest of Universal. I'd suggest heading over the The Simpsons area, maybe ride Men In Black if the line is short, and then a ride on ET before heading home.
All that should be quite do-able in a day, and you'll get the full Potter experience plus a taste of both parks non-Potter content.
Other tips: Make sure to do the regular lines of Gringotts and Forbidden Journey at least once as they're feature packed, but use single rider lines for subsequent rides as they go much quicker. For food, just grab something when you feel hungry, either Three Broomsticks or Leaky Cauldron are great, so just go to whichever one is in the land you're in when you're hungry. The lines move very quickly in both restaurants, so don't be put off by the crowds.
Make sure you try the butterbeers - frozen is the best, but they also do a regular soda one and a hot drink, all are delicious. Just don't stand in the long lines to buy them from the outdoor carts - you're much better to go inside Leaky Cauldron or Three Broomsticks and you should be able to walk straight up and order one, but many people don't know this as they think you have to get a meal instead of just drinks.
Another secret tip for the ice cream - the line at the ice cream shop in Diagon is always long, but 90% of people just want to try butterbeer ice cream, yet the line is for all the other flavours too, but you can get Butterbeer ice cream at the Hopping Pot on the other side of the alley, without having to wait in a long line.
Generally if you a see a long line that's not Journey or Gringotts, be suspicious as whatever it is people are waiting for can probably be purchased at another location with no line!
