When the weeks get long and busy, when the world seems like it's creeping in to keep you from housekeeping, focus on the kitchen and the bathroom(s). As long as you have someplace to cook a good home-cooked meal, and you can take a shower and brush your teeth without stepping over clutter or having to stare at globs of toothpaste, everything else can wait until next week.
But if the next week and the next come around and you're still "just having a busy week," it's time to accept this as your life and start finding ways to get the rest of the house onto a cleaning schedule and back into rotation. Maybe it's letting go of the idea that you have to do all of something at once--wipe down the mirror while you're thinking about it, scrub the toilet later, sweep the kitchen without mopping or run the vacuum in one room at a time if that's what it takes.
For us, having a set schedule is what's really helped. Occasionally, the vacuuming gets put off long enough that it's just not getting caught up, but skipped. But since we vacuum twice a week, that's no big deal. Occasionally the "Big Scrub Bathroom Day" is "just get the laundry out, swish a brush through the toilet and wipe down the vanity, the mirror and shower and floor can wait until next time!" When you know the last time you scrubbed the shower and you know the next time it's scheduled to happen, it's a lot easier to give yourself a break every once in a while--and also to remember that you skipped it the last two times and it's time to focus on that before it gets out of hand.