When I learn songs, I don't usually think about the notes after I've read them, once I've played it through following the sheet music, I usually have a good enough understanding of the song to follow the music in my head, and hit the notes in the scale according to the mood of the song.

If I know a songs in say, Ab, then I know which notes are diatonic, and can play those. It's easier for me to memorize a melody aurally, then translate that into notes. If it's a higher pitch, I play a higher scale degree.

Another thing I remember is the motif, which is a fancy word for riff. Songs usually repeat the same musical idea, so if I memorize that, then I can usually remember the rest of the song.

That's just how I do it. Play it enough, and it becomes second nature, until then, I use the music.

I'm interested to hear how other's go about this