I like @MacSparky’s implementation of a “reference screen.” I’ve been doing it for years myself, even though I never thought of it by that name.
My main computer is a MacBook Air. I travel several days of the month, so I can’t make do with an iMac 100% of the time. But most days the MBA stays docked in my home office at my desk. I have a 27" Cinema Display attached to the MBA, with Apple keyboard and an old Logitech trackball. The Cinema Display is my main display; I work at it all day and stand or sit front and center in front of it.
The MacBook Air is off to one side of the big display, and open, on a laptop stand. My eyes aren’t good enough to use the screen for long periods that way, but I can glance over quickly and look for alerts. The MBA’s built-in display is my reference monitor.
And what do I have open on the MBA screen? My email. I know that’s antithetical to the MPU ethos, which says you should only check email a couple of times a day. But I sometimes get email that requires my immediate attention, although of course I also get a lot of email that does not require my immediate attention, or any attention at all. With this system, I can glance over at my inbox every few minutes. If there is nothing requiring immediate attention, I go back to what I was doing. If there IS something that requires immediate attention, I pull my mail program over to the main display and deal with it.
Now I need to think about what else I might put on the reference screen. I wonder if there would be some way I could turn it into a screen of alerts, like the iPhone’s alerts screen. New emails, instant messages from Skype for Business, and anything else that I need alerting about. I know that MacOS has its own updates window, which can be activated by Ctrl-N or (IIRC) a swipe left from the right side of the trackpad. But I never remember to check that.
By the way: Like David, I have a standing/sitting desk – unlike him, mine is permanently at the tall height, and when I want to take a load off my feet, I sit on a tall stool. My standing desk is a regular desk with a 15" shelf unit on top of it; I highly recommend this configuration as being both practical, reasonably good-looking and INEXPENSIVE. You already have the desk, and you can get a cheap shelf unit at IKEA. Coffee table works too.
My setup as of a few years ago. It hasn’t changed much today. Not shown: The tall stool.
David recommends Mission Control for switching between open apps. Ive never warmed to Mission Control. I’m a fiend for Cmd-Tab, and lately I’ve discovered a tool called Contexts that makes Cmd-Tab even better – lists both apps and windows, you can search for the window you want to switch to, and more.