In order to take this position, you will primarily need the knowledge of foreign languages. What? It depends in which country you wish to serve. But in any case, you will need knowledge of the English language, and other, possible. In particular, Arabic, French, and other fairly common in the world.
Don't forget that you have to communicate in the native language and the language of a foreign country, and your language skills should not let you down in any of the cases. To speak in Russian, you should, as a linguist. At least competently, you should be able to use foreign languages, neither of which the accent cannot be considered. Because it can be taken as an insult, and besides, poor knowledge of a foreign language, or a bad possession impede communication. All of this can cause misunderstanding of people, and, consequently, of entire countries. Therefore, foreign language Ambassador to be perfect.
What else you may need in case if you decide to become an Ambassador? Of course, education. Moreover, the highest. Preferably MGIMO, although there are other educational institutions of similar level whose graduates have all the chances to this post. But still, even the best specialist, this post will get immediately. In order to obtain it, the person will have to work hard and establish a good reputation. Most likely, first he will have to work in the role of attache, Tokugawas over time to the Consul. Then he can be the Secretary, and further, if you are able to prove themselves well, Ambassador.
The main thing for a diplomat it is good reputation. Not having any, people will not be able to obtain such a position for a single simple reason. The Ambassador is the face of the state, and this man should represent his country, and only in the best light. And to make it can only the person whose reputation is not tainted. So that the honor and conscience for the Ambassador is no less important than education and knowledge of languages.
All this together gives the person a chance to get this high position. Of course, someone in such a career is easier - if you have senior friends or relatives. You can try to take advantage of this opportunity, paving its way to the top of a career is to try to make acquaintances and to support them. It's also diplomacy, and the extra practice will not hurt you.