The method I describe here is best to use if you don't have a zillion drops to do. It is also good for doing glass effects.
Items shown in purple have links to a more basic explanation of the concept or procedure.
Just be very patient with yourself as you do it, click on the purple text for further help, and keep your manual handy. Make a path into a selection. Use a channel to hold a selection. Do some hand airbrush work. Use the Stroke command.