After graduating college I was suddenly confronted with the fact that I would need to make a decision about this question. I had honestly never really thought it out before; when I was younger I just left all the important decisions in my life up to my parents while I spent my time having fun, so when I graduated college I had absolutely no idea what I should do for a career, and was very, very stressed out about it. I spent the next 2-3 years thinking about this issue almost every day, trying to figure out what to do and how to think about the issue.
I have now come to a very confident vision of how this aspect of life works. I've changed the way I try to think about work; now, whenever I try to make a decision, I imagine a small village in which one person farms, one person works metal to create tools the farmer wants, etc. Each person is creating things of value that increase the happiness everyone feels over an every-man-for-himself situation. So when I think to myself, "What kind of work should I do?" I now also think, "What would I want to do in that village?" This analogy has helped me 1) pull apart the different variables that should affect my decision, and 2) given me a clearer idea of what an average person's expectations should be (e.g. there probably won't be many jobs in the village called "food eater" or "bed keeper-warmer" because no one would trade away their goods for someone to do those things for them).
I think the main reason people get so stressed out about this issue is that our society has gotten to a point where younger people get used to having a lot of free time and having things provided for them without the need to earn those things. It ends up distorting people's view of reality. I think people need to adjust their thinking so that when they think about having a job they don't go "Darn, this is much worse than hanging out playing basketball with my friends for the rest of my life!"; instead they should go "Wow, this is so much better than fending for myself in a forest for the rest of my life!". I think one way to do this would by having people read a book that described the history of work, like the book "Marriage: A History" does with marriage. Another way would be to have kids working from a very young age.
Some of the factors that should affect your decision:
who you're working with (their culture; what they find funny, etc.)
the skills you'll need to make use of
where you will need to be to perform the job
how many hours a week you'll be able to and/or need to work
your income (per hour, per day, per year)
your chance of advancement
what you will think of your job (do you truly believe you are helping people?)
what other people will think of your job (e.g. being a plumber in the hamptons or a retired goldman sachs exec in smalltown USA)
whether the job will force you to be dishonest, secretive, or will force you to conform to some standard of behavior
Who you'll be working with
Different careers can have very different people working at them, and different companies within a single profession can have very different "feels". For example,
Coworkers' preferences for luxury items - If you go work for Goldman Sachs you will be surrounded by people who will be spending a lot of money on luxury items.
Coworkers' preferences for after-work activities - At a lot of office jobs people go out for drinks together when they want to hang out. Musicians may get together and play music together.
The skills that you'll need to make use of
Where you will need to be to perform the job
How many hours a week you'll be able to / need to work
Your other needs will affect the income you should aspire to: If you determine that your happiest path through life requires that you own a yacht, and you determine that the best way to get that yacht is through your work (rather than, say, marrying into a rich family), then you'll probably need to get a job that will give you the income necessary to get that yacht.
You should think about the amount you make per hour of work as well as the amount you make per day, week, or year. Otherwise you may get attracted to a job that pays a lot of money per year but doesn't pay a lot of money per hour; for example, one person calculated that people who make $160,000/year working for big law firms in NYC may only be making the per-hour wage of an employee at McDonald's if you consider the number of hours they need to work for that salary. Further reading on the importance of calculating your per-hour income: The Four-Hour Workweek
Your chance of / rate of advancement
The commute I absolutely hate the thought of commuting, but I've spoken to people who don't mind it. I can see it being nice or unpleasant depending on the situation. Commuting for an hour each way in rush hour in the city is dangerous and frequently stressful. On the other hand, commuting for five minutes via bicycle along a beautiful country road in Switzerland could be nice.
What YOU will think of your job Some people get into careers where they end up thinking of themselves as being a criminal, or a loser, or a sham. For example, I remember reading about a guy who grew up the son of an evangelist preacher; the preacher didn't really believe in God, but was just fooling people into giving him lots of their money. The son was trained from a young age to follow in his father's footsteps, but hated himself for it and so gave it all up (he was apparently making a lot of money doing it).
What OTHER people will think of your job For example, I've heard that many young people who are the children of asian/indian immigrants get pressured into becoming doctors or lawyers because their parents/siblings attach a lot of prestige to those jobs. For those children there may be a lot of other unpleasant things about those jobs, but one BENEFIT of such a job would be the fact that other people think highly of it.
This factor's importance may depend on the frequency with which you interact with other people. For example, if you live in a compound and never interact with people outside your immediate family, then you may not need to worry very much about what people outside your immediate family will think about what you do for a living.
You can even choose what people to associate with before you go into a given line of work, so that you never have to encounter the backlash that might come from continuing to hang around the people you grew up with. In fact, this may tend to happen automatically.
Whether the job will force you to conform / be dishonest / be secretive. - conforming, being dishonest, and being secretive can be sources of stress in your life. They may also allow you to obtain benefits that otherwise wouldn't be open to you. You should be aware of both the costs and benefits of conforming/dishonesty so that you can make a smart decision and not end up regretting it later. - think hard before going into a line of work that will require you to be dishonest or secretive. e.g. if you're a teacher or politician you have to be very careful about what you say/do. - also think hard before going into a line of work where you can be ruined professionally for having been arrested; some day you may want to punch a guy in the face. - beware any line of work that is wrapped up in bureaucracy and legal rules that will limit your ability to innovate. sam walton said that's one of the big reasons he steered clear of the cities (he gives as a specific example his attempt to do a hula on wall street after a very profitable year: he needed to get a permit from the police, he needed to satisfy the demands of the union representing the hula dancers, he needed to get permission from the head of the company whose building he was dancing in front of, etc. what should have been a 10-minute stunt took hours). my understanding at the moment is that there was a lot of innovation in the airline industry as a result of de-regulation; you might be best off looking for areas of work where you can experiment with new methods of doing things.
Don't commit to a profession based on a simplified idea of what the job is like: - My senior year in high school I interned for a neurology practice. I remember talking to one of the younger guys (40-ish) working there, and he said that his big disappointment with his line of work was that it was far more repetitive than he had expected/hoped. he thought it would be a bit more like detective work but it wasn't. i got the same impression from interning there and it really turned me off of medicine (although that was probably too-general a conclusion to come to).
Q: How can I tell if I'd enjoy a particular line of work or not?
- read autobiographies! Reading two books about Teach for America convinced me that I would hate it; reading about life as a biglaw attorney convinced me I would hate that too. - internships / temping / entry-level jobs are a fantastic way to get a feel for a career - being close to people doing that job (a family member, for example) - interviewing strangers who work in that field is another way
One thing that's occurred to me is that the amount that you get paid to do something is related to how widely-available is the information necessary to do that job. So, for example, web development is a skill that can be learned online; the information needed to do that job is widely available. On the other hand, many specialized jobs may require knowledge which is not widely available, but is instead passed from one person to the next. Those jobs may end up paying more.