Just as Old Vermin says, and as good friend, Mairead Nesbitt says PRACTICE, PRACTICE PRACTICE!! I also mention in my, posted, 'Ten Commandments for Musicians'!!!

NOW THIS IS NOT HARD...BUT PAY ATTENTION!!!!!!!!!!!!

Whether it be written, or by ear, THE GOAL is to hear INTERVALS!!!!!

Etch that in stone!!!!

For instance, take 'Over the Rainbow'. The first notes sung O--takes an octave leap("O--O Over the rainbow"). Learn to grab that sound, on whatever instrument you play, and KNOW that is the POSITION change, for an octave!
Now there are other songs, that you may be familiar with, whose FIRST TWO notes, are the 1-2, 1-3, 1-4, 1-5, 1-6, 1-7. Lock in those sounds!! and Those intervals, learn to grab their positional change!!!!
THAT WAY, as fast as you can imagine a melody, you can grab it on your instrument!!!!!!
IF you are ACCOMPANYING another player, you can ANTICIPATE the change, and you will KNOW exactly where to grab it!!!!!!!!(or even what fills you can do before you get to your 'target-note'!!!!!

I have, and still compose a great deal of music. This tool is invaluable!!! If you can imagine a piece of music, YOU CAN PLAY IT!!!!

Let someone else write the 'flyspecs' as to what you have played! If you play, using MIDI, just get the written print out.

LISTEN TO THIS PLEASE!!!!!!! From 00:45 to 2:20seconds into this video, LISTEN to what this young girl says!!!!!!!!

http://www.youtube.com/watch?v=DdZx1oIgAHk

Regardless of what you think of my views, whether you agree or disagree, on other subjects(BS Threads), what I have told you here, is absolutely the path!!!!!!!!!
You can thank me later....JUST DO IT!!!!

Any questions on clarification, FEEL FREE!! I'm ON YOUR SIDE, IN THIS MATTER!!!!!!

Warmest Regards,
Guest from Sanity