Fernando, I like this OP. I'm interested to see where it goes. I don't know if there are any secrets, and like most complicated issues there are likely a variety of reasons and causes. But as it is with most things there are likely a few things which show up routinely in the more successful, the happiest, etc.
So I will prime the pump. Many studies suggest there is a strong correlation between the happiest - and most functional economically and socially- countries in the world and the least religious countries in the world. The same correlation exists between the happiest and most functional and the least religious states. Many studies suggest there is a strong correlation between IQ and religion; the 'smartest' countries in the world tend to be the least religious.
So whether the measuring stick is happiness or success, maximizing one's brain power and energy towards achievable, realistic life goals seems to be a primary component. It isn't my goal to turn your OP into yet another us against them, theist/atheist OP, but the data seems clear, especially in the developed world.
As for me, I'm one of those on this site who has to pinch themselves from time to time to remind myself of all the things I have experienced and accomplished since exiting the Borg. None of those things would have occurred if I had kept my brain and energy wrapped up in a religious belief system. You can google the tenets for success. A focused mindset with vision and creativity and positive energy are near the top of all of the lists. When we were in the Borg, our focus and energy were on a fairy tale paradise. IMHO too many are still meandering around attempting to replace the fairy tale with yet another.