I DON'T! Do it all, I mean. I promise, it gets easier in some ways once you're past the infant stage. But I'm always clear on this subject: there are limits to how much I can take on and I will not sacrifice my health and sanity to do more than I comfortably can. That means that I don't kill myself taking my DS8 to 5 different extracurricular activities a week; just one. It means that I insist on time for myself most days - which is usually my hour to work out. It means that while I'm in school, on top of working full time, I'm not available to my DS's school as a volunteer. And it means that time with my DS frequently comes before housework, so I may or may not have dusted in the last two months.

Cooking healthy meals is important to me, but gourmet feasts aren't; I'm happy to make breakfast-for-dinner in the interest of saving time and making sure we still get a good meal together.
It's really about setting priorities and sticking to them; they'll be different for everyone, but we can all decide what's most worth the time we have available.