I wish I had the secret to time management and how to control the beastly amount of tasks that build inexorably in the typical product manager's "to-do" list. Alas, Product Management is one of those roles that collects the odds and ends of the organization, either by design (formally assigned), or by being the "buck-stops-here position.
While I can't solve that problem, I can share two of my secrets that I have used a long time in my career:
Avoid scheduling meetings.
Minimize the number of meetings you attend.
Really, it is that simple. Unfortunately, this is something that is extremely difficult to do in practice. In fact, in many organizations there are tools and processes to simplify the creation of meetings, all to "streamline" or facilitate the process. Un-ironically, this just leads to meeting proliferation.
However, I have found that almost universally, many meetings are not necessary. If you can accomplish the same result with a phone call, or walking to someone's workstation for a brief chat, or an IM exchange, just do it, and send an email on the result.
Or, if it is a weekly/periodic update, just drop it into an email and be done with it.
Sure, some people will feel that they have been cheated out of the dynamic of gathering in a room to discuss a topic. That there is some meeting etiquette to follow (agenda, note taker, a leader, a parking lot, yada yada). But, most of that isn't a requirement.
If I have to schedule a meeting, I have a few rules:
Keep it short. Really, I wish that Outlook defaulted to a 30 minute block instead of an hour. Or that it was convenient to start at the quarter hour. I hate meetings that are all 1 hour long.
Detailed Goals in Invite. A paragraph or less that explains why there is a meeting, what needs to be decided, and what the result will be. If people need to do pre-work, I will add that (or customize an invite per person). This way, there is no excuse for not being ready to make a decision.
Crispness. A meeting has a purpose, and that purpose only. If we begin straying, I am strong enough to table the discussion, and refocus the meeting. Every organization has at least one person who deflects the intent. Shut that person down (or don't invite them, even better!)
Not really amenable to a numbered rule, I have a 5 minute rule. If the key person is 5 minutes late, we cancel the meeting (unless they are far higher than me on the pay scale). There is nothing like keeping a room or a conference call full of people idle.
Once, a place I worked had a daily production stand up. A 15 minute meeting at 8:00AM. No chairs, and all the department leads had to attend, or send a representative. The rule was if you were even 1 minute late, you had to put a dollar into a jar. It was amazing to see directors running through the halls to avoid the shame of dropping a dollar into the jar.
How many meetings?
For invitations to meetings, it can be difficult. What is a reasonable meeting load? Is it 4 hours a week? 10 hours a week? Or, like my boss, > 40 hours of meetings a week?
While you can easily go about 30 hours a week in meetings, juggling back to back as well as double/triple booked slots, that makes it difficult to be effective as a product manager.
My belief is that on the average, if you as a product manager are spending more than 50% of your in office time in meetings, you can't be effective.
Learn to decline meetings. Really, it's OK to just say no, particularly if they are routine, or the dreaded status meetings. Why oh why can't they just build a dashboard, and send it via email, so that people can ignore it in their inbox, but instead feel compelled to have a weekly "update" meeting?
Naturally, there are some exceptions that define the rule:
If you have direct reports, schedule (and keep) regular, 1:1 meetings. This is vitally important to both your staff and yourself. It forces the ongoing alignment. If you can't do this, you need to talk to your management team about whether you should have direct reports.
Force your direct supervisor to schedule (and keep) a 1:1 with you. Half hour every other week should be enough. Drive the agenda yourself, know what you want to cover, and be firm about it. I am astounded at how many of my managers throughout my career tried to sideline this.
Meetings are a necessary evil. Modern collaboration tools, geographically distributed teams, and matrixed organizations pretty much assure that they have to happen. You can see the influx of meeting invites, and your calendar getting packed from before 8:00 AM, until well past 5:00 PM, and feel helpless.
Learn to control the inbound meeting requests, minimize the meetings you schedule, keep them short, and invite only the crucial people. Smaller groups can get to a decision quicker, and then get out of the way of progress.
Do discuss the meeting load with your manager in your 1:1's. They will be supportive of protecting time to work on your key initiatives, and provide air cover for some pushback.