The faster way is kinda hard to explain, but an effective way is using lots of filters together. But because that is a pain in the ass, I wouldd sugest just doing most of it by yourself...how?
1] The first step would be making the main drops over the image (New layer) in white to have in mind the direction. Remember always to do it as straight lines...works better.
2] Start to put into the body the wet effect...Do that by making the surrounding of the drop in fading white, being more dense in the top or in the direction of the rain if you get what I mean. Inside of the drop I tend to use a soft gradient in 20% opacity of white/blue.
3] New layer with a black and white graident (Lineal, Direction of the rain too) Then use Sprayed Strokes (5,25 for the values)
4] Erase in straight line part of the gradient over the characters.
5] Play with it and try other things, it's easy. Don't be afraid of using colors.
