Two ways that I know of
1. Lift weights or do any sport (martial arts if I may recommend). Testosterone is involved in muscle growth, thus the testes produce more testosterone when needed. Be aware though, this is no quick, permanent fix because that's impossible. You need to keep lifting weights/doing your sport to keep that testosterone floating into your circulatory system. Make it a passion or hobby. Doing these kind of activities also increase your general health if you do not suffer from inherited diseases such as decreased immunity, muscle atrophia etc.
2.Take risks sometimes and increase gradually the number of times you take risks daily or weekly. This will also increase your levels of testosterone. Don't stay too long in your comfort zone. When you feel you've been passive for some time, take some action and do something risky/challenging. You said your father was a gambler? He's taking quite the risk, ain't he? It's the testosterone boost that he's feeling. He feels ALIVE and PRESENT. I believe that all men and women master one ability in particular: to be too much in our head. I'm guilty of that as well. But how do we cope with it? Many ways: drinking, gambling, lifting weight and so on.
Now, I don't advice you to become a gambler or alcoholic, but do stuff that is CHALLENGING AND BENEFICIAL to you. Like what?
-Hit on a girl -> lay a girl
-lift heavier weights or do more repetitions
-set a challenging and beneficial goal for yourself and try to achieve it within a month. Afterwards, set a new goal by your new standards.
These three examples have one thing in common: putting you in difficult situations to expand your comfort zone, but not allowing you to stay in that comfort zone forever. When you have been in your comfort zone too long (by your own definition), it's time to move on and expand it further. Imagine if you only kept hitting on girls, but never laid them. Or if you kept lifting 10 pounds but never 20. Sounds boring, right? Progress is key.
Personally I would suggest any martial art in which a belt system is fundamental such as karate, judo and taekwondo. Why? Because it takes YEARS to earn your black belt. It took me five years to earn my black belt, and it felt so great because I had been working so god damn hard to achieve this. The pleasure came to no end. But it didn't stop there: I kept setting new goals after that - not only in my sport, but in every other arena as well. Goals that required patience because it would take months or years to achieve them. I think
this article about dominance and the winner effect is what you need to read to understand my perspective and how testosterone is involved in all that.
Since I don't know who you are, you must find out yourself what is challenging and beneficial to you. Yeah, you could try to win the Candy Crush series within 24 hours. That is indeed a challenge, but how is that beneficial?
Also if you're very new to self improvement, you might not know what is challenging or beneficial to you. But you won't know unless you try something, right?
Finally remember: to challenge yourself is supposed to be fun
start with small foreseeable goals, and save the big ones until you're comfort zone is expanded to the right level
