You should also try to avoid windy days. If you are working with a slow shutter (see tip #2), you don’t want the trees to be blowing about and blurring the background in your photo.
Waterfall Photography Tip #2. Experiment With Shutter Speeds and Carry a Tripod.
You have surely seen the soft wispy effect photographers create by shooting flowing water at very slow shutter speeds. This is a popular technique and has great impact for some photos. However, it is not the only method you should try. Some photos can look great, but if you do all your photos this way it can become boring and repetitive. Also, the wispy effect just doesn’t suit every waterfall. In my experience, cascading waterfalls that tumble over rocks and have several levels look great at slow speeds. I usually a shutter speed of one second. However, waterfalls that fall straight down over a ledge into a pool usually look better with a bit more definition; try a speed of about 30/sec or 15/sec. Experimenting with different speeds will always get you the best result in the end.
Regardless of the effect you are after, you should always have your tripod with you for waterfall photography. If you are in the forest on a cloudy day, the level of light will be very low, and you may find yourself forced to use very slow shutter speeds whether you like it or not.