For the Irises, clip out the flowered stems, cut the leaves down low in autumn (though you don't have to), for lilies, take the tops of the flowered stems off, leave at least half the stems with leaves behind till they start dying off.

With Bearded Irises, I just cut off the yellowing portions of the leaves as they happen. Due to our long growing season, Lilies here often put on a wave of growth from the younger offsets and bulbils in late summer, but that doesn't normally result in a second bloom. In most of the UK, that's probably not going to happen.