Any tips for someone visiting a water park for the first time?

Get a really good idea of exactly where you lay your stuff down. Look around and memorize what's nearby. I can't tell you how many times at Blizzard Beach/Typhoon Lagoon I'd put my towel, shoes, bottle of water, and sunblock on one of those beach chairs, went to a water attraction, and then could not find my way back to my stuff! I could have sworn it was RIGHT HERE! Nope.

Oh, I never thought anyone would steal my stuff. I just couldn't remember the exact spot.

As for sunblock, remember that it takes about 15 minutes from application until it's working full-strength. So put it on before you even get into the parking lot. And re-apply. Even a cloudy day is going to turn you into Elmo if you're not careful.

Pre purchase tickets. Leave important stuff at hotel safe, but bring some cash. Bring lots of water and some snacks. Food is expensive so check their food policy. Bottled water is usually okay. Bring water proof phone case if you want to take photos in the water. Theft could be a problem. Thus, no valuables.

At Volcano Bay, link a credit card to your Universal Orlando account in advance (you can do this via their app), and you won't need to bring cash or credit cards to the park. You can use your TapuTapu to pay for everything. (Unless you're buying alcohol. In that case, you'll still need an ID, too.)

Ditto on the sunscreen. I fried during the cloudy afternoon I spent at VB.

I like Aquatica so why not skip Blizzard Beach for Aquatica. You are already going to Typhoon Lagoon (Disney) and BB is also Disney...

Now when going to Volcano Bay you have to park like you are going to Universal, assuming you have a rental car and take a bus to this water park.

Also, Typhoon Lagoon and Blizzard Beach have free parking...

I can't say specifically for Florida's waterparks, but for waterparks in general everything that applies to a regular amusement park still applies. In addition, I'd add the following:

-Wear your swimsuit to the park under your clothes. This will save time and allow you to beat the crowd to the rides. If you will not be going directly back to your hotel afterward, you'll want a change of clothes for when you are done, but otherwise you could wear your swimsuit both directions.
-As soon as you get inside, claim a spot by spreading your stuff on one or more lounge chairs (usually you'll want one per person). Make a note of where you are so you can easily find your location later.
-Bring as few valuables as you can (usually, I just bring my car keys and enough cash for the day). Your best option is to use a waterproof pouch, but if that's too small you can hide it at your lounge chairs (bury it under clothes in a bag) or rent a locker if necessary.
-Wear waterproof footwear that is easy to remove and hold. In general, you will be required to remove your footwear on any waterslide, so make sure you can remove it quickly and hold it in your hands without difficulty. I like to use sandals that I can strap to my arms while riding a slide, but anything that is waterproof should be okay. If you are visiting in the morning and have a reasonable heat tolerance, you can go barefoot in the park, but when the ground gets hot you'll want footwear to avoid burning the bottom of your feet.
-Reapply sunscreen every 2-3 hours. It will wash off quickly in the water, and you can get some pretty bad burns on areas that aren't normally exposed. Also, avoid riding body slides immediately after applying sunscreen as those will wipe it right off your back if it hasn't fully soaked in.
-Lastly, be sure to take breaks and drink plenty of water. In my opinion, waterparks are more tiring than theme parks because you'll be climbing a lot of stairs to ride the slides. If you have a full day, try to get on as many slides as you can in the morning, then spend the afternoon relaxing and re-riding your favorites if the lines are reasonable (waterparks don't see the crowds regular theme parks do, but due to lower capacity a line will take 2-3 times as long as a similar length line would at a theme park).

I agree that the less you take, the best. I've not been to Volcano Bay, but I have to say I absolutely love Typhoon Lagoon. My best advice would be to get a lounge chair that is close to an entrance point to Castaway Creek, the park's Lazy River. My favorite spot was always the entrance point just past the backside of the wave pool. It was close to the shark reef swim through, but that attraction is no longer in operation. I always liked being close to the lazy river because you can hop in and float around the park to the area you are interested in going to.
There are plenty of F&B options in park, but I always preferred to stop at a Publix on my way to the park and pick up a sandwich from the deli. You will want to confirm that they still allow people to bring food in, but they did when I was going frequently.
Most important thing to remember is a day at a water park is intended to be a day of relaxation. Chill and relax.

Oh one more thing, Make sure you check the Water Park hours also..

Volcano Bay looks like they are staying opening much later in the summer, closes at 9 to 10 PM..
Some water parks close earlier...

VB also has been selling out, they only let about 6K in there daily..