How long can humans work before there (total) productivity goes down. Assuming there is a lot of variation per individual and per task, how to determine this number for yourself?

The best answer to the question "how long can people reasonably work" that I know of is this post by Lynette Bye, and the answer is there  that we don't know, there is not much evidence out there, and we should experiment ourselves.

And if there is no literature, would it make sense to set up a study ourselves?

I'd love to see a more evidence-based look into different types of meditation techniques if possible.

Also, I'd like a better breakdown of how much exercise, what types, and for what benefits. (E.g. how much should you exercise for optimizing for well-being vs longevity? To what extent does it matter if it's high intensity exercise for well-being vs low intensity?)

I would be really interested in someone collecting counterexamples to popular narratives around sleep, nutrition, long work hours, exercise, happiness, "negative" emotions and so much more. "Research" in these areas seems to be propagating socially/virally and common beliefs are selected for desirability (and hence often suitability to be used as an excuse) than for anything else. This is often worsened by science being a social process and researchers pushing cluelessly toward these socially desirable results. Kind of a collective "psyops".

How to get really good at incorporating new habits or behaviors into your life and stick to it (maybe something like "cultivating discipline"). I've found external accountability fixes a lot of this, but it would be cool if the motivation could be internal.

I would be interested in evidence-based ways to fight procrastination and akrasia. Ideally, these techniques would have long-lasting positive effects so that once you learn them and practice them, they become natural. 

This is sort of vague, but I'd like to see more about whether/how to induce mindset shifts.  For example, for decreasing procrastination, there are sort of "quick fix" methods (e.g., blocking websites, creating routines) and others that try to get you to change your mindset or motivations (e.g., Nate Soares's Replacing Guilt).  I'm not sure whether there is any research on how these two broad methods of self-help compare, but I'd be interested to hear.  For example, to what extent are these approaches complementary?  In the procrastination example, does blocking websites effectively decrease people's urges to find distractions, inducing a mindset shift, or does it simply cause them to find new distractions?

I imagine many of us spend a lot of time sitting and staring at screens. What would make this less bad? What are some alternatives we could do sometimes? What are the health and other costs and benefits compared to possible alternatives? 

For example, doing a phone call and walking vs a zoom meeting. For one on one meetings that seems like it would often be a good idea. For small groups, maybe you need an agenda and do a rotation on everyone's thoughts/updates as you go down each item, to cut down on awkwardness/time wasted not knowing who is about to speak, and make sure everyone gets a chance to contribute what they know. I used to do meetings like this years ago but I completely forgot since now it seems like we default to video conferencing automatically.

Thanks for this!

Some ideas:

How to improve social skills

How to learn faster

Optimal diet

Best nootropics and supplements for mental health, productivity and so on.

Reducing anxiety

Reducing depression

Effective collaboration

Optimal time management

A couple have already mentioned it but I'll repeat the request for nutrition advice. In particular: As a vegan, what supplements (aside from B12) should I be taking? Are there any that may be harmful? Are there any evidence-backed dietary interventions that improve cognitive performance?

 - Easy ways to change one's environment to change one's behaviour (block sites, automatically transfer x% of the salary to a savings account...). That's probably the lowest-hanging fruit in this field: easy to communicate, easy to implement, usually very effective, basically no side-effects and one does not need to make an effort to change his/her behaviour.

 - Examples of rules that can be used to change one's behaviour and stick to it (allowance to eat meat only on Saturday), and tips on how to get back to the rule once broken.

 - Effective ways to improve reading speed. And resources for slow readers (e.g. text-to-speech softwares in different languages, tips on how to retain information).

 - Tips on how to find out one's strengths and weaknesses, and advise on what to improve when (when does it make more sense to improve a weakness and when a strength?). It is probably easy to generalise the tips so that one can help others identify their strengths and weaknesses.

It is important that the feel of the project is realistic. Popular (bullshit) self-help normally implies that one can do almost anything regardless of his situation. This is often net-negative as, for example, not acknowledging time constrains often leads to too much commitments and a dramatic decrease in outcome-quality.

Including well-researched but not yet well-known health tips (I'm thinking mostly but not exclusively about nutrition and mental well-being) could be a good asset, as medicine is often quite slow up-taking new research. However, it is tricky (where is it not well-known?) and delicate (can induce people not to seek professional help when needed, who can benefit of the tip? can it backfire?), so I don't think that one should start here.

I was always curious about biofeedback (GSR/HRV/EEG).