Water Skiing Sportswear
The first thing you'll need, assuming the boat and skis are ready to go, is a water skiing wetsuit. For many skiers a simple bathing suit serves the same purpose, but this comes with a few drawbacks. Most importantly, your water skiing wetsuit will stay on no matter what. A loose swimsuit can be lost in a flash if you hit the water at high speeds, and there's nothing more embarrassing than having to climb back into the boat in your birthday suit.
A wetsuit also protects more of your body during those falls, and let's face it, if you're new to water skiing you probably will fall at some point. It keeps you warm when skiing in colder waters, and it doesn't make that loud, annoying flapping sound.
The next item you'll need to go water skiing is a life jacket, also called a personal flotation device or PFD. It's not just the law, it can save your life. A PFD will keep you afloat if a particularly hard fall knocks you unconscious. They can even be fashionable. Those clunky orange vests are almost a thing of the past; today's PFDs come in every possible color, and some of them are as comfortable as your favorite shirt.
All that's left now is to accessorize. Get some good gloves for gripping the tow rope and handle. You'll probably want some goggles or sunglasses as well; that bright sun will be even brighter when it's shining back up from the water's surface. If you don't want to ski barefoot get some sport sandals, aquasocks or deck shoes. Deck or boat shoes are great for walking around on wet surfaces.