Overgrown clumps of herbaceous perennials can be divided now. This will invigorate them and improve flowering and overall shape. Lift the clump and split the outer area of the clump, discarding the centre which will be the oldest part of the clump.
Don’t worry if you are not able to do this now, some can wait until next Spring, just make a note of which ones need attention.
Continue to deadhead plants to prolong the display. Why not treat yourself to some Spring bulbs that you can scatter around the garden or put into pots to give some brightness at the beginning of next year.