Questions

I have a garden that is very overgrown with shrubs of all sorts i.e. flowering shrubs and shrubs that look like they will stay green/yellow for the whole of the Winter. I wont be able to do anything with it until the first week in September (just bought the house), can I cut back the shrubs by a third when they stop flowering or do I have to wait for the leaves to fall off I'm not sure if they do fall off? Can I give them a good cutting in January because they make the garden look small, its deceiving.