You should prune shrubs every year, or you end up with exactly the problem you've got now.
Different plants have different requirements for pruning, but now is quite a good time of year for most shrubs. Basically you need to prune after flowering, so for anything which has just finished flowering, go for it.
Can you get a gardening book out of the library and look up the shrubs that you have? Or do you have any gardening friends who could tell you?
Sorry, I don't know what your plum-like things are - sounds intriguing!
take a cutting of each shrub to your local garden centre. I've done this with an unknown tree which cropped up in my back garden, and they were very helpful. They gave me the name of plant, how to care for it, size it would grow to etc etc.