Write down the chord sequence over which you will play your solo. From this chord sequence, determine which keys and modes you will use for your solo. For example, if the backing chords are C major, A minor and G major, you can use the scales of C major and A minor. From these scales you can select modes, such as A aeolian. Modes are inverted scales; they contain the same notes as the major scale but in a rearranged order. Modes add a new tonality to a familiar scale. Refer to the cycle of fifths to determine all possible key combinations.
Prepare transitional phrases. Play each scale and each mode that you noted down and identify and write down the notes that are shared between them. These notes will work over any chord in the sequence. Use them as a means of moving from one scale to another.
Switch from minor to major. For each minor scale, note down the relative major. For example, the relative major of D minor is F major. By switching from minor to major you can alter the mood of the solo from melancholy to cheerful. The relative major scale starts three frets higher on the same string. For example, the relative major of G minor is B major. G minor starts on fret three of string six; B major starts on fret six of string six.
Reference the top-line melody. Transcribe the vocal melody from the song and play it on your guitar. Use the two-handed tapping technique to double the speed of the note changes. By taking the familiar melody and adjusting the tempo, you introduce melodic familiarity but add a rhythmic twist.
Incorporate dynamic changes. Although heavy metal solos are traditionally fast and furious, you can achieve an arresting and intriguing sound by lingering on one or two notes. The third guitar solo in "Sweet Child Of Mine" by Guns 'N Roses features a series of sustained notes that last for half a measure each. Guitarist Slash lets these notes ring before unleashing a rapid minor scale pattern. The impact of the minor scale pattern is intensified by the contrast of the slow ringing of the preceding passage of the solo.
Resolve on an unusual note. Solos typically resolve by finishing on the key note. This adds a feeling of finality to the musical phrase. Push the boundaries by finishing with an interrupted cadence (See References 4).