I do not pretend to have all the answers, but I think it might be worthwhile to write down some suggestions that I found myself giving to friends and family over the years, about how to achieve a degree of happiness in life (regardless of where one lives).

NOTE: this is written from a western perspective, with a caveat that migrating to a prosperous country (not always synonym with a western country, but let's face it - almost always) will help massively in achieving happiness.

To start, what does one need in life to be happy?

According to Maslow's hierarchy of needs, one has (in order of importance):
a) Physiological needs (food, water, shelter etc)
b) Safety needs (personal security, financial security etc)
c) Love (intimacy with someone else, family love etc)
d) Esteem (self-respect and self-esteem in general)
e) Self-realization/actualization (the need to reach our dreams, such as becoming a parent, a politician, a businessman etc)

The main way to achieve a and b is to land a good-paying job. This will allow one to cover his physiological and safety needs, while giving enough financial freedom (over time) to try and achieve one's dreams later on.

What are fields that pay well enough?
a) Medicine (almost all sub-fields)
b) Engineering (still almost-all, but less than Medicine. e.g. do not specialize in Civil Engineering in the West)
c) Statistics, math and related sub-fields (keep away from theoretical subjects, gravitate more toward actuary statistics and you are golden)
Honorable mentions: IT and Economics-related bachelors have much lower chances at achieving a great salary, but still better than let's say Philosophy

For those who don't know, I am an Italian actuary but I travel (USA, UK, Germany, France and Singapore primarily) very often for work-related reasons; I can say with a decent degree (pun intended) of certainty that the situation is the same all over the place in regards to qualifications.

Going back to the list of needs, Love and Esteem can only be attained individually - sadly there is no magic trick to find the right person to be happy with. Having said that, one can watch out for red flags.

Love:
Dating too much outside of your comfort zone is not the way to go if one wants a long-lasting relationship (but it totally is if one cares only about having fun!). This is due to the fact that in such a relationship one of the two partners will have to change (sometimes radically) in order to make it work - this will lead to resentment toward the other partner and will be cause of issues later on, be either a break-up or resentment and unhappiness.

NOTEs: by "Comfort Zone" I mean your culture, set of ideas, ideals - whatever you want to call it, the "ensemble" of one's own beliefs. While race is not a huge issue in the dating world, when the culture is too divergent it may very well be another factor creating tension. Practical example: a Nigerian guy and an Eskimo girl will have issues due to their divergent cultures the same way that an Italian guy will have when dating a Singaporean girl (or a French guy with a chinese girl etc, you get the point); while the fact that one's SO is of a difference race might not be an issue for the two lovebirds, it might very well be for their families/friends/group of peers. Depending on the importance their respective cultures (and the people themselves) place on said other groups approval, this might cause problems in the relationship itself.

Esteem:
Esteem is something that only you can give yourself, since it must come from within and not without. If this is not the case, we got a problem in the form of attention-starved individuals - and nobody likes a desperate man/woman, remember that, be it on the work or in the dating field.

Having said that one can raise his own self-esteem by feeling "accomplished" and/or "helpful". You can do this by various means - e.g. take up a hobby and get very good at it; open a business and be relatively successful; find something you excel at and practice it; become a volunteer and help your local community...the possibilities are endless. Remember only that lazyness is the mother of all evils and you should be good to go.

Regarding depressed people (not the fake-emo bs, but ones who actually got real issues), I would really advise to get professional help. Sometimes even just moving abroud (or in another part of the country you live in) might help. Get well.

Self-realization/Actualization:

Now THIS is where one finds true happiness. If you reached this stage, you have covered all the basic needs and can now finally focus on yourself and your own life. Once more, I cannot tell anybody how to live their lives and how to achieve one's own self-realization, but I can surely tell you that you shouldn't think of this as a task to be completed - simply live your life! I assure you that you will find something that will make you happy doing. Once you found it, just keep doing it! It is that simple.

Many people say "I do not know what to do with my life". Bullshit. They know perfectly what they would love to do with their lives, but are either too scared to actually do it, or messed up somewhere along the way (unwanted children, loss of job due to mistakes, it could be anything) and thus cannot physically do it. The solution to the first is "Just do it!"; to the second issue "Do not screw up in the first place!" or, if you have already screwed up, simply solve the issue and move on!

NOTE: while I do not personally condone this, I will admit that there are cases in which the only way to win and move on with your life is to run for the hills from your problems - especially if the rules are stacked against you. While the honorable and right thing to do is to live up to one's mistakes and just hit issues head-on, sometimes even doing the right thing might land us in jail and/or make us face punishment from authority. In this case, there is no shame in admitting defeat and starting over.

Miscellaneous tips:
a) Always try your best at everything you do - not doing so will make you feel cheap and unaccomlished.
b) On the other hand, if you try your best and still fail, do not blame yourself - if you truly gave it all, rest in peace with yourself.
c) Sometimes admitting defeat is the only way to move on. Do not be the retard that cannot ever admit to be wrong.
d) Do not screw up. Seriously don't - it is always easier to avoid making a mess than solving one. It costs less and takes less time.

Just a final thought from myself that can be applied to any culture - the issue of children and marriage.

If one wishes to marry and put up a family, please make sure that you are not bringing kids in this world just to give them a miserable life, while becoming miserable yourself (before anyone think "won't affect me if I run away" - yes it will. Even if no one every catches you and/or you suffer no physical consequences, enjoy asking yourself for years "what could have been had I not ran away". The easiest way to achieve this is to get a job in one of the fields I listen previously.

On the other hand, think long and hard if marriage and/or a family life is for you. I can tell you (from seeing this happen time and time again, all over the world) that many find out years later that this is not what they truly wanted and that they got married only because they were acting purely on emotions. This is a sure way to screw things up.

And with this I conclude this little post. I just hope it might help you all brothers and sisters.

PS: take note of what I wrote earlier - if you find that where you live will simply not provide opportunities to be happy - move! It is that simple. The easy way to move is to get a decent degree and obtain a love-term visa for specialist work. It is easier than one thinks if you graduated in one of the fields I wrote earlier in the post.