for rain and fire, I use a programme called vision lab studio, it lets you add all sorts of effects, from explosions to rain drops that you can customise to your liking. as for doing teardrops, I've heard that you can use small pieces of glycerine or some jelly like substance that will work.
Something I have heard also works on a low budget is using small pieces of PVA glue and allowing them to dry. They will dry clear and can be fixed onto the face of a plasticine character easily when pressed on.
Before I forget, another way to make a ball float in mid air (this depends highly on the set) you will need a green background for chromakey, and you will need to paint the support for the ball in the same shade of green. This way, when you swap the green for an alternative background, the ball will appear to be in flight.
Hope this helps