Book tickets on-line in advance - that way you skip the queue outside and can go straight in. Use Kellogg's cereal codes to get a free adult ticket for every child ticket bought.
Pay in advance for parking. So much closer, and great to only have a short walk to the car at the end of the day.
Go the back of the park first, and work your way to the front.
Remember, not everything opens at the one time. Some areas open later in the morning. Go to the dragon rollercoaster as soon as the Nexo Knights area opens. You can get a few goes on it before the queues build.
Bring your own picnic. Food there is awful and over-priced. Also bring lots of drinks, sunscreen and a small towel to wipe off wet seats.
Bring your own disposable ponchos. They cost £3.50 each there.
The shops stay open well after closing time, so don't bother going to them during the day.
Pick up lots of maps. They are on display units just after the turnstiles into the park, but didn't seem to be anywhere else there.
Enjoy!