The Major Scale
To become a good improviser, you will need to be familiar with the major scale, as most other scales are derived from it. A major scale is a pattern of eight notes in alphabetical order that produce the familiar sound:
The C major scale contains these notes in the following order:
The distance between each note is two frets except for 
and 
where the distance is only one fret.
The distance of two frets is called a tone, indicated by T.
The distance of one fret is called a semitone, indicated by ST.
The major scale is probably the most common scale used in music. Here is one octave of the C major scale in the open position. Make sure you know it from memory.
The notes of the C major scale have been used in thousands of melodies ranging from Classical music to Folk, Country, Jazz and classic Rock.
The natural notes in the open position are all from the C major scale, even though the lowest note of the pattern is E and the highest note is G. The key note C occurs twice and is indicated with a square around it. This pattern can be described as the full open position fingering of the C major scale.
C Major Scale In Open Position
Here are the same notes written in standard music notation and tablature. Because the lowest note in the fingering is E instead of C, a different effect is produced. This effect can be used to create a variety of sounds from the scale when improvising.
Depending which chords you are playing over, it may sound best to start on any of the notes in the scale. For example, if you were playing over a C chord followed by a D minor chord you could play the scale starting on C for the C chord, but start on D for the D minor chord.
