You can start by looking for a book about native shrubs (I have found one for the Southeast US, for example). Not all of your shrubs may be native (there are plants that invade wild spaces), but it will be a start. Here's one from 1966 that you can get used copies of on Amazon : Recognizing native shrubs; by William Carey Grimm. Who knows? It may help. Ask your local/regional native plant society about books.

Identifying them when they are in flower is easiest, but identification through leaves is not bad. If you have a digital camera, posting questions on the Native That Plant forum here on GW is helpful.

Petride's book on trees and shrubs is good, but no colored pictures. It will be easier in the spring when they have leafed out.