To be able to pick up your guitar and play any melody you hear would be nice I guess!
To understand the relationship between the melodies you hear and the frets and strings you have to use to play these melodies is something you can practice in different ways. Here are some suggestions:
1. Play around with your guitar. Yes, that's right! Have a nice time with your guitar! First of all because it is fun and you probably play the guitar first of all for this reason.
This means that you try out things on the guitar. Play notes and listen how they sound. It doesn't really matter if it is fantastic melodies you create. The important thing is that you gradually will learn how notes, strings and frets relate to each other.
2. Learn scales. Scales can be played for many reasons. One way is to develop a better understanding of the fretboard.
To accomplish this you should as soon as you have learned to play a scale on the guitar try to use it, experiment with it, try to create melodies with it, play patterns and so on.
3. Learn music theory. Well, this sounds a little bit intimidating maybe. But music theory can be as simple as knowing the names of the notes on the guitar. Take a few notes at a time and practice playing them on the guitar as you say the notenames aloud.
4. Learn easy melodies. Yes, very easy melodies like Mary Had A Little Lamb and other melodies with few notes in them. Then try to play the melodies starting on a different place on your guitar fretboard. This is a very effective way to learn to understand the guitar.
5. Transpose songs. You will develop your ear and your understanding of the relationship between chords by transposing the chords of the songs you can play by heart to different keys.
Let's take the song Tom Dooley as an example. It contains only two chords in it's most common form. If you play it in D-major it will be D and A7. If you play it in E it will be E and ...well you can figure it out by yourself.
Try to play Tom Dooley in the key of C and see if you can figure out the chords.
To hear a melody and then be able to play it on the guitar is really both fun and of great use to a guitarist. By trying these tips you might find yourself a little bit closer that goal!
