If you play a musical instrument and are just getting into jazz music with its improvisation, here's a piece of advice for you. Because not everyone has a good ear and/or a good memory, reading from the music score is still important when you are jamming with others. Also, when you are just starting to dip your toes into jazz, learning music theory is a great help, and for that you need to read music. But having said that, once you are familiar with a song, do try to do away with the score especially at a jazz jam. There are several reasons why you should gradually get to a stage where you can play some jazz standards without looking at sheet music: 1. Jazz jamming depends on spontaneity, and interaction between the players. The surest way to kill the spontaneous element is to look at the score while playing. You should at least be able to play the 'head' [melody] without referring to the score-else don't go up to jam or worse still call the tune. As for the chords, which are the underlying structure, and backdrop for the musicians to improvise upon, try to memorize them. At the most you should only glance at the chords while playing as a prompt and a quick refresher in case your memory fails. But to play note by note and follow each chord while improvising is to lose the groove, and affect the other players if they are not like you.
2. You are not going to use the music score as a crutch for ever in your musical 'career'. When you are so dependent on the score you will not be able to develop your musical intuition. Music is an art, and is dependent on your emotions and how you express them. Jazz improvisation is NOT playing an arpeggio or running scales over the chord structure. It is your interpretation of the song. When you read from the score, you cannot feel the structure of the whole song and the music does not flow, and your improvisation does not flow. The best improvisation is done when you are comfortable and know the chord progression and structure of the song, and you can concentrate on putting 'feel' into your improvisation; and make it melodic as opposed to 'technical' . Many musicians can do a technical improvisation with meaningless runs up and down the scale but few have the ability to craft a melodic and meaningful improvisation. All the most popular jazz guitarists are popular because their music sounds tuneful and meaningful e.g. Joe Pass, Kenny Burrell, Howard Roberts, Anthony Wilson.
3. Many jazz songs especially the standards have common patterns in their chord progression. If you are less dependent on sight-reading you will one day find yourself more able to recognize these patterns and be able to participate in jazz jams without feeling nervous. One way to remember the chords in a song is to see if there is any logic in their progression and recognize the pattern. One way to remember the melody is to hum it to yourself. The best way to do both is to hum the melody while visualizing the chord changes. The ability to identify chords and feel chord changes is not so difficult. Most people with average musical sense are already able to play simple pop or folk songs with 3 chords e.g [all examples in Key of C Major] C, F, G7. A little more development in musical intuition may add ability to sense a D7. Or a C, Am, Dm, G7 progression. Still more development means ability to recognise an E7 or even a B7. Then soon you can recognize a F#m7b5 to a B7 to a Em. Or even be able to use a turn- around like Em7, A7b9,Dm7,G9 or change a C, C7, F, G7, C, to Cmaj7, Gm7/C9, Fmaj7/Bb9, Em7, A7b9, Dm7,G13b9,C69. Then you will jump for joy when you can see in your head a Db7,or a Bb7 instead of a G7. All this is merely an extension of your ability to recognize and feel C,F,G7 and its changes.
Many baby boomers grew up strumming the guitar and then left the guitar behind sometimes for decades while they pursued their careers. Now that they have more time, some want to go back to learning to play a musical instrument. They also want to learn to play more sophisticated songs like the jazz standards and the bossa novas, whose chords are more interesting, harmonies more complex and more challenging. If you are a baby boomer and like many baby boomers want to progress from the pop and rock music of your younger days to jazz, a software like Band-In-A-Box [ http://www.pgmusic.com ]will be a great learning tool. You can also write to me for a collection of jazz standards and bossa novas files with chords, melody,lyrics etc in Band-In-A-Box format.