1. If you wear glasses, I would wear one of those cords that keeps your glasses on.
2. Make sure anything loose in your pockets is removed before riding. At the bottom of the pretzel loop I have seen smashed ipods, PDAs, cell phones, even a pair of sunglasses. One time loose change rained down on me as a Manta train went into the pretzel loop. I left SeaWorld 37 cents richer. <g>
3. If you're sensitive to excessive G force, I wouldn't ride. Personally, I don't know why G force is seemingly so important these days--almost passing out isn't my idea of enjoying a coaster.
4. At the bottom of the pretzel loop you're on your back (where you feel most of the G force). Do actual manta rays "fly" on their backs? Dunno. It's a feeling I have yet to get used to.
5. Take the time to enjoy the ride line. It's themed nicely, and you can see various rays and other sea life along the way.
6. If you're in the park with someone who isn't riding, ask that person to go below the lift hill. He or she can take a very up close picture of you strapped into the car as you ascend.