I have tested a lot of hacks for productivity.
Some worked, but were too complex to implement in the long run.
Some didn't work at all for me.

From now on, I'll write more about this topic and my experiences and approaches.

Today I'll start with my most important hack for productivity:

Use a Schedule (properly!)

That doesn't sound very original.
Many people already use a schedule - in a less than optimal way.

My biggest mistake was that I only entered external appointments,
i.e. appointments with other people - meetings, dinners, etc.

This put my personal appointments in the background and gave them a lower priority.
First I took care of all other people, then I took care of myself.
Why didn't personal appointments deserve a place in the schedule?

Treat your personal me-time appointments with respect, give them space in your schedule!

Example:
A person says that his/her health & fitness is very important.
At the same time, this person has hardly any related appointments in his/her schedule. Eating, moving, sleeping - put it in your schedule.

Implementation:

Step 1:
Create a blueprint schedule with an entry for every time block that lasts at least 30 minutes. We don't want to become micro-managers, otherwise the system becomes too complex.

Question: Why should I do that?
Answer: To get an overview of your daily activities and whether goals and implementation match.
Example: Goal: To be healthy & fit. Implementation: 5hrs sleep, 10mins eating at the desk and 5mins of walking from apartment to car => Goals and implementation doesn't match.

I use Google Calendar.
You can enter repeating appointments:

Example:
2200-0600: sleeping
0700-0800: grooming, mobility, breakfast
0830-0900: commute
0900-1200: work, part 1
1200-1300: lunch
1300-1700: work, part 2
1730-1800: commute
1800-1900: dinner, relaxing
1900-2000: gym
2000-2200: friends

This could be a blueprint schedule for Monday through Friday.
Also do this for Saturday & Sunday.

Question: Saturday & Sunday?
Answer: Sure. Do you know this feeling when weekend passed by quickly? That's because many people live an unconscious life.

Step 2:
Adjust the schedule daily to get the actual data of your life.
If you see some empty blocks, try to remember what you did there.

Step 3:
Review your actual schedule at the end of the week and look where your time actually flows to. Does this contribute to reaching your goals?

What are your best productivity hacks?