I would be inclined to clear all the under brush and remove dead and dying
growth, and not be to drastic in the first instance.
Remember once cut down you cant stick it back if you change your mind.
look to see if you can work out what you have and when it flowers. If you
cut out spring flowering shrubs now then no flowers till 2005.
Some things like Forsythia can be cut back slowly through the winter, and
the stems brought indoors and pot into water to force the flowers, forsythia
cut first week of Dec should be in flower indoors for Xmas, same for a few
other spring flowering shrubs.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk