Keep a book. Make a list of your to do items. If you're a fancy techno schmuck keep it on whatever electronic device you've got on your belt, and type away at it with your thumbs, I don't care, but keep a list. You have to be the guy that never "forgets" to do something. And you can't be that guy without a list.
Find a way to rank order the list. Unless you're an unimportant dumbass in an overstaffed cesspool, there's going to be multiple items on your list. As you add items on the list you need to know which ones to prioritize on.
Here's how I do it. I think I saw it in one of those inane management classes. Next to every item on my list, I jot down an alphanumeric code of sorts. That's a two digit code - first digit is a,b,or c, in order of importance and the second digit is 1,2 or 3 in order of urgency. You should be spending most of your time on the items coded a1 and the least on c3. in fact if your code begins with c, consider delagating it. I also put in a commit date next to the task if it exists.
Every day at the end, last 15 or 30 minutes (see previous chapter), go through your list, reorganize your list. Strike of the completed ones, reevaluate their urgency, and judge your progress to your commit dates. As a very last resort, after your have exhausted all your wiles, you should recommit the ones you think you need more time. Recommiting should be considered a sin if your code begins with an A.
Never ever be the cause of a meeting reschedule. Ever. It's disrespectful.
The only reason for a reschedule should be an explicit instruction from your boss, or safety or HR. If another meeting being rescheduled impacts a meeting which then you have to move, then as far as possible, dont.
Get your shit together at work. You have to be viewed as a consistent person who does what he says he will. Do not take on more than you can chew and then make lame excuses. Do not whip around other people's schedules because you forgot you had something else to do.
I know you're thinking that there are many middle managers who do this. How come they're successful then, you're thinking? Well check out how many of them go PAST that middle management purgatory. And think of how many senior (C-Level) managers you know that dont keep to a schedule.
There.