Clematis – how to prune for the winter

My clematis flowered purple late in the summer, beautiful. It grew upwards and only spread out one side. I trained it up a trellis. Its died off now, brown. I am afraid to cut it back incase it dosnt grow as much next year. if you keep cutting them back each year, where do you cut them back to?Also does it grow faster each year the older it gets?