Thanks for all the tips, everyone. I'm going to go through your responses and come up with a plan for myself, based on all your advice. I appreciate the START NOW perspective, although the first thing that came to mind was, I've already started "now", many times! I will check out Flylady and the other sites you all posted.
I will just add that while clutter was one big example of simple living tips, it's not the only issue. Keeping the house clean (obviously linked to clutter, but not the same issue), getting tasks done efficiently, not feeling stressed, getting ready for work on time, not losing things (amid the clutter...)... I feel like those things would also provide me with a lot of peace. If there are any other tips for simplifying life, or recommendations for books with practical focus (as opposed to vague and inspirational), please post those too!
Actually, Bakari, you mentioned something that I've been wanting to do for quite a while: downsize to one bowl, one cup, etc. that I always use and wash right away. What is holding me back? 1) 30 years of habit, putting dishes in the sink/dishwasher and going off to do something else; 2) The fact that they always say dishwashers are much more efficient than washing by hand (That said, I lived without a dishwasher for five years recently, and I still let the dishes pile up, so I think it is mostly habit); and 3) I can't put all the dishes under the bed until the rest of my family is on board with my "one object system" in the kitchen, so the extra dishes will remain in the cupboards, tempting me each moment... but I think one practical thing I can do is go out to the thrift store and buy a distinctive plate and bowl (to tell them apart from the others) and start just rinsing them each meal, one day at a time. Maybe I'll aim for a week and see how it goes. There, I've thrown down the gauntlet!