Planning and organisation.
Don't forget the saying "if you fail to prepare, then you should prepare to fail".
Both OH and myself are planners. It saves so much time, energy and stress in the longer term as you tend not to have last minute panics, run out of things, get caught out, etc.
OH is worse than me. Planning a day out is a military operation for him, down to planning what we want to see, where we want to go, how to get there, finding car parks, finding places to eat that cater for all our dietary quirks, checking attraction opening times, etc. By doing that, we don't get caught out so the day runs more smoothly. By "route" planning, we don't waste time doubling back on ourselves.
With children, the key is keeping them informed, tell them what we'll be doing, set "milestones" during the day, i.e. we had a habit of getting an ice cream mid afternoon, DS knew that, so he wouldn't be whinging for one in the morning. When we were going somewhere that DS (when very young) may get bored and start acting up, such as a restaurant, we'd take something with us to occupy him, such as a couple of matchbox cars, or a small drawing book.
I look after the home, and plan shopping with a list on Excel of all the things we will ever need. I print off the blank list, have it on a clipboard in the kitchen, and then mark things off as we use them, so next time I shop, I replenish what we've used. That's not just food, it's cleaning materials, and "specials" such as snacks, ice lollies, etc. By doing that, we never run out of anything, so we won't waste time doing "extra" shops for things we've run out of (which also waste money as smaller shops are more expensive).
As DS got older, we'd have informal "family meetings", often at mealtimes, about places we wanted to go to, holidays, events, etc., so he'd be involved in the decision making process, which made for more pleasant days out, holidays, etc., as he'd have felt part of the process, was more aware of what we were doing (or not doing), and why, etc.