pruning soldiago / goldenrod

If you mean Solidago, then when it has finished flowering, you may cut the old flower stems down to the ground. Or if you like the flower heads then wait until spring and cut them down then.

Unless you want a lot of goldenrod, you may want to cut down the old flowering tops ASAP(it can spread quite effectively), or the whole plant, as suggested by owdboggy....
I read somewhere that this plant helps to extract lead from the soil...Bonus if you live in an old house which was probably painted with lead paint for years...