It feels the same as touch-typing on a keyboard. My brain envisions the pitch I want, and my fingers know where to find it. Musically though, pay attention to

It feels the same as touch-typing on a keyboard. My brain envisions the pitch I want, and my fingers know where to find it. Musically though, pay attention to the feeling of notes relative to the root of the key you're in (as opposed to in isolation). You can envision a keyboard in your head and map the movement of pitch to movement on the imaginary keyboard. There are only so many notes in a Western major scale; eventually you will find that notes from a melody fall into place on this imaginary keyboard as you hear them, and you can translate that into finger movements. This won't come overnight. It took me about ten years of being musically active to be able to figure things out by ear; another ten to be able to do so on the first try (i.e. hearing pitches as easily as words in a conversation). These periods were punctuated by a solfege class which I credit with helping me develop the latter ability. If you are still in school take such a class if you can find one.