Managing up is the practice of managing one's own manager. It means managing their expectations, understanding how to best communicate with them, knowing what they aren't good at, how they like to be involved in projects, and what kinds of metrics and expectations they're beholden to.
Bad bosses really need it, but so do the good ones. The goal of managing up is to make your job and your boss's job easier.
It takes time to learn how to manage your boss (every relationship is different), and the way you relate to your manager will change over time. I've had bosses where our relationship started out sour and then improved; with others, it soured over time and then was salvaged; and with others still, I've managed to remain simpatico throughout my tenure. Managing up is about a personal, professional relationship in which both people need to succeed, and need the other to succeed as well.
Get to know them
Does your boss prefer face-to-face conversations or emails? Phone calls? Texts? Slack messages?
Are there questions they always ask? Questions like, how much will it cost? How long will it take? Why should we do this? What is the ROI? These questions indicate what's important to them.
Does your boss prefer you come with a single solution or a stack-ranked list of possibilities? Do they want to review proposals before they go out, or do they expect you to fly solo?
Understanding your boss's working style and preferences helps you manage them.
Understand their job
Your boss' stress often comes from their expectations and goals that come from their boss. Take the time to understand who their stakeholders are, what kinds of details they are responsible for, what their bosses expect from them. By understanding this, you can produce work that helps them do their job better (who doesn't love that?).
Here's an example. I track some of my metrics on a weekly or even daily basis. My boss likes to see these, sure, and I am required to report them to her, but her stakeholders (investors) look at trends against a longer timeline. When I report weekly numbers to her, I also throw in month-over-month and year-over-year change, plus context about how and why we're seeing these trends. So when an investor pops up and wants to know how such-and-such is doing, she has the context she needs at the ready.
An important part of managing up is managing your boss's expectations. Let's say they come to you with four projects they need completed by the end of the month. You know that you can realistically complete two, maybe three, in that time.
Be honest with your manager. Not only for your sake (overworking is a dangerous precedent to set), but also for theirs.
You might say:
I can realistically get only two of these done by the end of the month. Otherwise, quality will really suffer. It looks like A and B will have the biggest effect on the business. I vote we start with those two. If we have more time, we start working on C.
If you come up against mismatched expectations, ask your boss to prioritize the following elements as they relate to the work: quality, speed, and cost. (And no, all three cannot be top priority.) Whichever ranks third gets cut.
Sometimes you'll have a boss who doesn't totally get what you do or isn't heavy-handed in your day-to-day work. Giving them plenty of context on your work, like your regular tasks, how much time it takes to complete them, how much it costs, what tools you use and why they're important, and how long it takes to see results are all so, so important to managing up.
This will help them make more realistic requests of you, set better deadlines (there, your job just got easier), and see you as an active work partner.
Tell them how to use your skills
Even an observant boss may overlook some of your skills, and they may not know about the ones you want to develop. You should be an active participant in your career development.
Tell them what you're really good at and volunteer for those tasks. (And deliver.) Talk to them about what you'd like to be really good at and volunteer to play a role in those tasks.
Remember that you're more than your job
It becomes a lot easier to manage up when you set a healthy personal distance from your job, especially if you have a difficult boss. Wrapping your identity in your job or career is a dangerous practice.
I've had good bosses and bad bosses, just like I've been a good boss and I've been a bad boss. There will be days where your boss is off the rails and there will be days when you're, ehem, not at your best. Give them the benefit of the doubt, just like you would hope they would do for you.