I'd say: Get rid of stuff. Not by doing a lot of elaborate planning and organizing, but by always having a trash bag and a donation box around, and making a point of dropping things into them and getting them out of the house when they're full.
Because that's the core of simplifying your house - getting stuff out of it. It's tempting to, say, set out to reorganize your closet, and pull everything out of it, and count up the stuff, and make stacks for mending and summer and winter and so on. But doesn't that usually end up with all those stacks sitting around for a few days, and then all getting stuffed back in the closet, with little real progress made?
So an alternative is to open your closet and find _one_ thing that you can either trash or donate, and carry it to the trash bag or donate box. And then do it again. And again. And when you're interrupted or distracted, your progress remains - those items are still in the trash bag or donation box.
And the same in the kitchen - open the cabinets, look around, and find that Tupperware bowl with no lid, and put it in the trash. Look around again and find those six fast food souvenir cups that you no longer care about and put them in the trash. Pick up that cast iron skillet that you thought you'd season and use, seven years ago when you bought it, that's just been gathering rust since. And put it in the donation box. And, again, when you're distracted or interrupted, that progress is still maintained.
If you keep on doing this, one thing at a time, reminding yourself and reminding yourself to deal with one more thing as often as possible, then your storage areas will start thinning out more and more. Someday you'll have to "organize", yes, but that's the less important part - it's the getting rid of stuff that's really the key.