Compare the following sentences:
I normally think of ようになる as expressing a gradual change. So maybe I studied just a little bit two years ago, a bit more last year, and this year I'm studying hard. I suspect that this is not what 勉強するようになった actually means though. Can ようになる describe a sudden change of state, i.e. today I decided that from now on I will study Japanese?
What about はじめる? It was suggested to me in a comment to one of my answers that はじめる is "to start doing something at the moment and implies that the action will not be continuing for a long time". I always used to think that はじめる simply meant "to start" with no restrictions on time etc. Now I'm not so sure.
In short, when should I use はじめる and when should I use ようになる to describe starting something.