Before to go a waterfalls place you need some preparation.
Except for the camera Lens, you need Tripod, ND Filter, Tissue paper, shutter release, raincoat for the camera.
Normally we see waterfalls images look silky smooth.
It can possible to use slow shutter speed. So you need to set our camera slow shutter speed of several seconds or longer. Slow shutter speeds create the ghosting effect, making the subject appear smooth and blurry, which is exactly what you want.
Set the camera ISO smallest number. It also increases image quality.
See your camera ISO 200, 100 or 50 (some cameras have costume settings for 50 ISO)
Set your camera aperture lowering or high f/ number. Lowering aperture decreases light to pass through the lens. You can set f/11, f/16 or f/22
Use ND (Neutral Density) filter
Already you have set the lowest ISO, set aperture largest aperture (to pass minimum light) and largest f/number. This combination helping you to set a second or more second exposer. If still, you cannot get a second or more second exposer. So in this situation, you can use ND Filter it will help you to go one second or more second exposer. Normally you can use ND4 or ND8.
We using an extremely slow shutter so it is not possible to handhold a camera to avoid camera shaking. If you have no tripod you can put your camera on stone or any hard things, which is not shaking. But for better composition and better results, you must use a tripod.
Raincoat & Tissue
Normally big and high waterfalls are making draggling in this surrounding area so you need a camera raincoat to save your camera & lens. In exposer time must check your front lens or Filter for water drops, so wipe it with a tissue before every single expose.