Pruning advice needed?

I have a very large bush in my garden, (long green leaves, large round yellow flowers in the summer) no idea what it is, I pruned it in the spring before it began to leaf again, it took a long time to show life and although there are lots of leaves in the centre of the plant most of it has remained just wood. Do I prune back to where the leaves are or leave alone. If I prune it back it will be about a tenth of its original size.