Cutting back perennials

I haven't been on in a while...back to school (I'm a teacher)...ahhh.

But I know that its time I start thinking about pruning back some of these perennials, but I'm not sure what to do and I really don't want to kill the stuff.

I have a lot of little flowers...salvia, yarrow, "speedwell?", coneflower, blackeyed susans,butterfly milkweed, shasta daisies, foxglove, beebalm. From what I gather, it is pretty much THE mix in any perennial garden. SHould I cut these back now (the black eyed susans are totally black and dried), or wait until the spring.

I also have tons of day lillies that have a lot of green left in them (I'm pretty sure I need to wait on those). But I also have a Peony bush that isn't looking great (maybe some powdery mildew or something on the leaves), and a really thorny busy with large deep red rose like flowers (way thornier than my climber roses), that looks like it needs to be cut back too.

Most of the stuff I could find individually on-line, but I am just not sure about all of these little guys. I would really appreciate some help.

Oh yeah, and one more thing, I have a lot of clematis vines (one with really big flowers that the previous homeowner had the plant tag for, so i'm good on that), but the ones I'm worried about are the ones with smaller flowers. The flowers have been gone for a while, but most of the vines still have green left on them. THey didn't flower for very long this year, and I'm not sure when to cut them back either.

I know its a lot, but I inherited this huge-beautiful garden and I just want to be sure that it all comes back next year! HELP!

Hi Keborda,
It's always a guessing game with perennials. Should you leave them to get the last little bit of nourishment from the leaves, or should you cut them off.
I usually wait until the first frost, and then I chop all my perennials down to about 6 inches. I do that so that I can find them in the spring, but they haven't all turned to mush and slime.
As for the clematis, you can cut them as much or as little as you like. If you leave them as-is, you just need to pull off the dead stuff next spring, where they didn't send out buds. If you cut them back 1/4 or 1/3 they will bush out at the top, and keep a slender bottom. If you cut them at about half-way, they'll send up lots of new shoots from the base and be bushier on the bottom.
Pick a nice sunny day that's not too cool and enjoy the weather.
Catherine