Lynn reading the Universal forums will help you a lot. Also you can go online to the Universal Orlando website and look at a map of the parks which includes what rides are located in the parks. You can look up restaurants located in the parks and Citywalk and their menus and Park hours, this will help with your planning.
There is no super planning needed for Universal.
The last two weeks of May are when things start to pick up for sure and Volcano Bay is opening on May 25th so hopefully it won't be very busy during your time there.
Some tips:
You didn't say if you would be staying onsite or not? If you decide to stay onsite good options are RPR, PBH or HRH.
All of these hotels will include unlimited Express pass with your stay which is a great perk. Unlimited Express pass will allow you unlimited front of line access to all the rides except Forbidden Journey, Escape from Gringotts and Hogwarts Express.
Also another perk of staying onsite is admission to what ever park IOA or UO that is opening early for onsite guests. Onsite guests get to go in one hour earlier then offsite guests.
If the early park is IOA then Hogsmeade will be open for onsite guests to ride Forbidden Journey, Flight of the Hippogriff and Dragon Challenge.
If it's Universal Despicable Me Minion ride will be open and Diagon Alley will be open to ride Escape from Gringotts.
I looked at the website and IOA has the early opening for onsite guests during your time there. May 13-18 is 8am, May 19 is 7am and May 20-21 is 8am.
Express pass allows one front of the line access to each ride except those noted above. Unlimited Express allows unlimited rides on all the rides except those listed above. The maps on the Website will list all Express pass rides also. If you do not stay onsite and the parks are busy you can purchase the passes in the parks. The Universal Website lists the cost for the Express pass and the Unlimited Express pass.
If the park is not busy and wait times are not long a lot of people do not purchase Express passes. I stay onsite and always have Unlimited Express pass.
If you do not stay onsite be at the park of your choice at rope drop.
The most popular areas of both parks is Hogsmeade in IOA and Diagon Alley at Universal. If you are Harry Potter fans you will be wowed by these parks.
Make sure to purchase park to park tickets so you can ride the Hogwarts Express between the two Potter Parks.
See the Ollivanders wand show at Diagon Alley. There is one in Hogsmeade also that tends to be busier.
Have a butterbeer at the Hogshead Pub in Hogsmeade.
Maybe lunch at Three Broomsticks in Hogsmeade.
Wonder through the shops at Hogsmeade and Diagon Alley.
If you are blown away by Hogsmeade wait till you see Diagon Alley.
Make sure your camera batteries are charged up or that you have plenty of room on your phone to take pics because when you see Diagon Alley you will want to take some pics.
The Dragon on top of Gringotts bank breaths fire about every 10 to 15 minutes and you will see people standing in the middle of the walk waiting to catch the perfect pic.
Wonder through Knockturn Alley and enjoy its cool darkness as well as Borgin And Burkes.
You will see people doing magic tricks throughout Hogsmeade and Diagon Alley with their interactive wands. These can be purchased at both Potter parks and in the big Universal store and also at the Universal stores at the resorts. There is map included with the interactive wands showing you where all the magic trick spots are located. There is also a metal medallion on the ground in front of the magic spell sites.
So if you are a big Potter fan you can choose the wand of your favorite character or if you are lucky you could be chosen for the wand presentation at Ollivanders where the wand picks the Wizard.
My pic for restaurant meal not to miss at IOA is Mytho's.
At CityWalk it's Toothesome Chocolate Emporium, Cowfish, HardRock, NBC.
There are great stickies on the Resorts.
This will get you started. If you have anymore questions ask away. Someone here will jump in and help you.