Don't be afraid to experiment! With digital cameras, you can now store an incredible amount of photos. Try it out! Don't be afraid to set up your camera at a stream one day and play around with the effects to see what kind of photos you get. It can be a great way to learn what works, and what doesn't.
Use speed when capturing your pictures. If you take too long, the subject could move, the sun could move behind a cloud or it could start raining. Anything could happen, so don't delay. A camera which allows you to make quick photos will give you the best results.
When working around subjects that are moving a lot or are totally in action, you need to focus on capturing the moments by keeping your trigger down. These kinds of moments can not be recreated and there are no do-overs. Keep your eye on the areas at all times and keep shooting.
A much simpler way to freeze the water drop with one flash. This video shows all the gear and camera setting needed to accomplish the task.