The only productivity hack that i found useful is:

Having a uninterrupted time in working flow.

Ask yourself: When was the last time you had three or even four completely uninterrupted hours to yourself and your work?

You need to attention to the quality of the time that you have for a certain task. Let's say you have about 4 hours to work on something. You are more productive if you not let the time to be sliced into eight separate 30-minute slices, or even worse and more then that!

Also remember that, this is not only the matter of an hours. It can be expanded to the days. What do i mean by this?

I mean, if the task is daunting enough, it's MUCH more productive to put 2 consecutive days completely to work on that, then to do it in 2 hours everyday throughout the week.

This rule of thumb is emphasizing on the importance of the working flow and the cost of context switching. This is something that i felt thorughout my day to day work.

For me, anything more than that feels like an efficiency trap. That's it.

UnRelated

The concept of the importance of uninterrupted time can be applied to any other activity as well as formal working hours. Whether it's Lifting some weights in GYM or Reading an interesting book or even spending quality time with a someone you care about.

It might depend on the kind of work that you do, But uninterrupted time is the single best thing for quality output and genuine enjoyment that i found; for almost anything in my life. And this is something that i desperately going after.