I think some people are born lucky. My keyboard player is not a folkie - but he can play all our barn dance tunes second time round. I've even given him a tape of a tune that I was having difficulty with and he produced a set of dots. Me - it takes ages to get a tune in my head - and then sometimes I find I don't have the right notes on my basic melodeon.

I find with the melodeon I think I know a tune when I can play it in both D and G, as a waltz, reel, and 6/8. ( 5/4 is just showing off). I then find out how fast I can play it before the notes disappear. Then its probably ready to play out. However, over time I have got better playing by ear and with the music.

For me, the first bar of a tune written down helps to remember what the tune is.
FloraG