Once upon a time a clever and very successful DCM gave Madam some advice.
The subject was Careers with a capital C, and he said two things that she has found to be extremely useful in the ensuing years.
First, he said, it's okay to not share others' ambitions. You might feel weird or wrong if your A100 classmates salivate over, say, an extended tour as political counselor in Brussels or ambassador to London or Tokyo, while you hunger for a DCM-ship in Ulan Batar or econoff in Ouagadougou. But you aren't wrong. Just as one FSO's hellhole is another's paradise (and vice versa) one's dream job is not another's. It's okay to want what you want.
Second, no FSO's professional journey is straightforward. Look, the DCM said, for steps that will be fulfilling in themselves and will also carry you obliquely toward your goal, that dream job. Move to the right bureau or to the same area of the world; find a job that will get you the language; get training in that subject or one closely related; read up; tell your boss what you want (if he or she is trustworthy); volunteer to fill a gap or to go there to help if a disaster occurs. If you can, go there simply as consular cannon fodder very early on. It is extremely common for an ambassador, DCM or counselor to have three tours in his or her favorite country: as a JO, at mid level, and for that final dream job. Such progression gives an alert and professional officer a markedly superior understanding of the place and its people; it also introduces the officer early on to local fellow worker bees whom he or she will meet later as equals at the peaks of their own careers.
What this all means is simple: know your objective; be patient; gather the tools, the expertise and the reputation for professionalism; luck favors the prepared mind. So does the broadest possible thinking and planning.