Many brought up points about keeping it clean and this is very much true. They prefer "Strait laced" folks who don't drink, and of course don't do drugs. Supposedly Mormons and very devout Christians make up big chunks of the intelligence community for these reasons. Mormons travel abroad, many pick up a language while on their missions; as well, they are strait edged, trusted, and they get recruited heavily by their fellow mates.
My buddy does intelligence for the Military here. I have no idea what he
does, but I have a basic picture...somewhat.. from the bits and pieces he has told me over the years.
His day to day life sounds very easy, but boring. Really just monitoring systems with evrey now and then as he calls it "something gets kinda of crazy once a month, maybe twice.. but only lasts about 4 days.. then its back to coffee runs and browsing the web".
He said at first they really mind fucked him and admits getting brainwashed with a lot of Army kool-aid, he has woken up now, and just views the job for what it is. Its a stable drone-desk Govt job with amazing benefits, and thus he is chilling.
Advancement on his side is strange as they take into account rank promotions among your corps and other stuff that would be tied to him doing missions and tours which he has stopped doing. But he has mentioned there are ways to get ahead via internal Certs they offer so you can take on more skill and responsibility.
His experience is unique as its Canadian and Military, but it likely paints a picture of how day-to-day desk life would be for your typical intelligence worker.
Next, a girl I worked with also had plans to be a "spy" (She must think its a movie). Her game plan so far has included a internship with NATO (I guess these are offered all over their member nations, so look into it), and she has a undergrad criminal justice (minor French), masters in geography, and is fluent in Italian. Her plan B is to go full Diplomatic-International Aide route if the CSIS plan does not work.
There are knowledge branches which information is sources. This diagram give you a picture of what core competencies you can focus on for your skill set while having other things such as languages to help make you a sought after candidate: