The first step in landscape photography of any kind is to scout the area a bit and determine the best angle and composition. If the waterfall is in a shady area, consider whether you might want to use HDR to get the full effect. Consider taking shots at different focal lengths. Sometimes a close-up will turn out beautiful, other times that wide angle shot that includes the colorful foliage will be your best bet. Do you want that creamy white look, or a crisp, sharp picture of the water as it tumbles down. Do you want to be at the base of the falls looking up, at the top, or maybe level with the top but at a distance. Ideally you will get all of those shots, to appeal to a wider range of people.
It is not quite a universal rule that shooting raw images is better. There are some instances where faster write times are needed to prevent buffering. But in general, it is better to use raw images, or raw and JPG. Raw images provide the maximum information, thus allowing you flexibility during post processing.
Is a tripod necessary?
A tripod is an important piece of equipment to have if you want to take high quality pictures. It is not absolutely necessary, but since good focus is important, you should have the stability that a tripod can provide. There are alternative devices that are perfectly acceptable, but some kind of stabilizing device should be used. Image stabilization that is built into lenses and cameras will help, but it is not a good idea to rely on them alone. When shooting long exposures they will not be able to prevent all shake/movement.
In addition, you should use a remote shutter release if possible, or use the timer setting on your camera. Shutter remotes are available in wired, IR, WIFI, or Bluetooth, depending on the camera you are using.
As with raw vs. JPG, it is an almost universal rule that you should use a low ISO
for landscape pictures. That is because landscape pictures are normally static scenes that can be shot with longer shutter speeds, so higher ISOs are not needed. The obvious exceptions would include times when there is motion of some type that you want to freeze.
To blur, or not to blur?
Getting a creamy, white smoothness is a classic look when photographing waterfalls. To get that look takes either the right timing, the right filter (a neutral density filer), or both. You want to get the shot during the time of day when there is no direct sunlight on the water so that you can get use a longer shutter speed. You can further increase the length of the exposure by using a neutral density filter. A neutral density filter is one that does not effect the color while still reducing the light that enters the lens.
If you want to create a dramatic effect that shows the motion in a different way, you can reduce the shutter speed as much as possible, or increase the ISO, or both.
Should I have a polarizing filter?
A properly used polarizing filter can help reduce the glare from the sun or reflections. It is important to understand the proper usage and limitations, though. For example, a polarizing filter is of no use when pointed in the direction of the sun. It works by being positioned at a ninety degree angle to the sun. It also will not help reduce reflections from metallic objects.
What lens should I use?
In photography circles it is widely believed that the lens quality is much more important than the camera itself. It is also thought that the skill of the photographer and his artistic interpretation of the scene is more important than any of the equipment used. That said, it depends on your budget. One of my favorite landscape lenses is a 50 mm prime lens that costs about $125. If that sounds expensive, you have not shopped for DSLR or mirrorless camera lenses. Not that you need either of those to take good pictures, but their versatility and flexibility make them the go-to choice for most professional photographers.
My choice among zoom lenses is much more expensive than that. I love my 24-70 mm lens for landscape photography because that is the focal range where I shoot the majority of my landscape photographs in. If I want to pack light I might go out with just that one lens because it has the versatility to be usable for most landscape shots.
What camera mode should I use?
Manual mode is my preferred mode to shoot in. But sometimes it is easier to shoot in one of the semi-automatic modes (Aperture Priority or Shutter Priority). When shooting landscapes you want to use settings that allow higher aperture numbers (smaller aperture openings) so that you get enough depth of field to keep the entire image in focus.