One of the best pieces of advice I can give to people trying to avoid the large crowds is, go early! Make sure to get there 30 minutes to an hour early so you can get parked, get walked up to the gate and get in. Once inside hit the big rides that you want to do that day and get them out of the way.
This works as most people are on vacation and no one wants to get up early. This means most people start getting to the park between 10am – 12pm, and then it is really busy until about 4pm -5pm when people start leaving early. So in the middle of the day is when the park is the busiest, so plan accordingly.
Early Park Admission
Typically one of the parks will allow one hour Early Park Admission for people staying at one of the on site Universal Resorts, or for annual pass holders (black out dates apply). If you happen to be one of these and can get in an hour early, this gives you a jump ahead of the crowds to get in the rides you want. Again, this only applies to one of the two theme parks, so check online to make sure which one.