Esslentially I think that's how I learn a tune in a session - find a note or a chord that fits, play that when it comes around, and extend out from that. I generally find soon enough my fingers know what to do, even when my head doesn't - I've a terrible head memory for tunes, where there aren't words, but my fingers seem to know their way round.

With words, writing them down by hand helps. So does singing while driving, using rather the same method as playing, just singing the words I know and stretching out from their. If I'm learning a song to sing it I tend to do it backwards, by which. I mean last verse first. That way as the song goes along it's likely to get more familiar, you're going home.