What to Expect in Waterpark

Many rides will have an age and/or height requirement.

Prepare to be climbing stairs for most attractions. If you're in poor physical shape, disabled or elderly this may present a problem.
Expect there to be crowded. Setting expectations before you arrive will help you tolerate the crowds and make it a fun outing. Areas of the park, including some lines, may have little to no shade from the sun.
Drink plenty of water. You should stop hourly for a drink of water and of course from the water fountain or concession stand, not the pool.
Some parks require you to rent inner tubes for the wave pool and lazy river. When you rent a tube you may also be able to avoid the line for waiting for a tube on rides that require them. Ask the park for details.

Final tips
If you're coming with a group of people or bringing the family then bring some cheap towels and set up a spot for the day on some of the park's lounge chairs. You can then return to this spot throughout the day to relax.

Look into renting a cabana for the day. While the price may seem pricey, you'll have reserved seats and shade, plus most parks provide a server for food and beverages and some have perks like express entry, complimentary tubes, towels, and sunscreen.

And the most important tip of all. Have a fantastic time!