Learn C# or Python. Not only do they have a large community, they are common enough in game dev. (As opposed to, say, Java or Ruby, which are generally equals of the two I mentioned, but are not as omnipresent in game development circles.)
First, learn all the basics (data structures, basic algorithms for sorting/searching/etc, basic IO, etc.) from complete online tutorials or books.
Then, learn how to build a basic game. Learn common game algos (ex: KD-trees) and patterns/architecture (ex: the game loop) while building a basic game.
At that point, you should have enough knowledge to be able to start self-guiding.