The basic idea for taking interesting water drop photographs is to find big drops after rain on a humid day with no wind, with attractive objects in the background. Then, all you need to do is to get the shot in focus with a nice composition.
The trick is to have enough depth-of-field so that the drop and the plant are all in focus while leaving the background sufficiently blurred so it does not compete for attention. Use f/8 to f/10 but you can go as narrow as f/18 too. Having the perfect focus of the object refracted in the drop is desired, but sometimes it is much better to have a more abstract picture with less focused colours.
Photograph/Steve Wall