For all its worth, I have my share of lifetime mistakes when it comes to time management. If I will think of it now, I might as well request for one big life reset.
Anyway, nowadays I think of trying to accelerate my phase like a metered cab. There is a calendar beside me, a spreadsheet file of priorities. And when I sit to do a task, I imagine to have just started my "cab engine," thus, my time is metered. It seems to make me accomplish more than simply doing it without the thought of this limit.
I also utilize the alarm clock more. Example, I time my cooking so I won't need to watch and stir with trial and errors. If it needs to boil at a certain period, only the clock would remind me to attend to it. It gives me spare time to do other things. The pitfall here is the mistake in encoding the timer. Other than that, practice makes perfect.
My very concept here is taken from the more sophisticated concept of PERT/CPM where every slack has to be filled in with another task for efficiency. It is just put into a more practical context. It's self-explanatory. Try it!