Hundreds of business books dole out advice on how to be a better manager, but the majority focus on how to manage from the top down. One topic that does not receive sufficient attention but is arguably just as important is how to manage not down--but up. The phrase "manage up" is as inscrutable for most junior PMs as a Rubik's cube. We all know we're supposed to be capable of doing this, but we often have no clue how to execute it in practice.
What is managing up? I like to think of managing up as feeling empowered to make decisions on behalf of your manager--and, therefore, the project. Before you can begin managing up, you need to focus on doing quality work with a smile, until the PM trusts you enough to afford you opportunities to make decisions, even if these decisions are small. An example of a decision might be prioritizing which assigned task is the most important. Another example of a decision could be responding to a client question independently.
Imagine you are a junior PM on a high-profile, fast-paced client project. The PM asks you to write a report, but her instructions don't make sense to you (likely because she is running from meeting to meeting and didn't have time to properly explain the assignment.) Even though the outline doesn't seem consistent with what you know about this client, you figure the PM knows more than you do, so you check her calendar to set up a meeting to discuss. Unfortunately, judging from her calendar, your PM doesn't have time for a bathroom break, let alone a discussion with you. The report is due tomorrow. Making the decision to modify the report--and explaining your thought process for why you did what you did--is a form of managing up.
Isn't managing the project manager's job? In the example above, your project manager should have made the time to meet with you to explain the assignment thoroughly and discuss potential approaches. In reality, this luxury may not exist. The client may come to you with a last-minute request. The PM may have been pulled into an unrelated meeting. Since human cloning and time travel are not yet viable technologies, you as the junior PM have to do part of the PM's job for them. Guess what: anticipating what your PM needs--and then doing it--is your job. PMs--your job is to practice letting go of those responsibilities that you don't personally need to own.
My project manager has so much more experience than I do. How does managing up help them? Just because the PM knows more than you doesn't mean they have to do your job too. In fact, it probably means that they shouldn't. If you felt 100% comfortable with what you were doing every day, you are probably in the wrong job, because it means that you aren't learning and growing. We have to learn to be comfortable with some level of discomfort. That being said, in the example above, owning the task of writing the report means that your PM has one less thing to worry about. That helps them do their job, and it consequently helps the project advance.
What if I make the wrong decision while managing up? Managing up is largely about trusting your instincts. If you landed this job in the first place, then your instincts are probably pretty good. But, no one is perfect, and especially if you have less PM experience, then you may make the wrong decision from time to time. When you are entrusted with a task, you can often make an educated guess about how to execute it based on common sense, project knowledge, and context clues. If you're still unsure, I would encourage you to ask yourself what would happen if you guessed wrong.
Will it create an ethical, compliance, or safety issue?
Will it result in a serious financial loss?
If the answer to one of these questions is yes, then it might be appropriate to leave that decision to someone else. If it's no, then remind yourself that the consequences of guessing wrong are likely inconsequential. Sure, you may get yelled at or need to do some rework to correct the issue, but that's a part of learning. No one's likely to blame you for or even remember these small setbacks. On the contrary, imagine what would happen to the project--and your career advancement--if you guessed right.