(But also, remember that cleaning with the right tool can be a zillion times more efficient.)
This can mean wiping down the sink with a paper-towel after you dry your hands in a public restroom, or wiping the rim of the toilet with some TP when you’re done peeing (if you haven’t yet been convinced that it’s better to just sit to avoid that fine mist of pee), or dusting the top if you notice it while you’re standing there. I also do this before starting a load of laundry—just give the machine a quick wipe with a towel that’s about to be washed, so that the clean clothes won’t brush against a drip of detergent or a line of lint. Basically just keeping things from ever getting gross without needing a dedicated cleaning day (or guest arrival, as I recommend as a hack in Advice: Having trouble keeping your space tidy?).
One of my favorites is keeping my squeegee (from Advice: the best way to wash windows) under the sink in the bathroom. I’m not the sort to be willing to manually dry my shower to prevent water spots like some folks, but I do have a huge mirror in the bathroom that inevitably gets splashed from washing my face and hands. Instead of waiting for cleaning day to scrub the mirror, I’ll just let the thing get fogged up from a shower and then give it a quick once-over with the squeegee and with 10 seconds of effort and a little attention, it’s back to looking tended to.