At the outset, the marking Tempo Rubato, Italian for, “stolen (rubato) time (tempo),” allows for some freedom to speed up or slow down the tempo. However, fluctuating tempo should never be erratic, or excessive, but done as an expressive response to other musical elements such as phrasing, dynamics, or melodic contour. Listen and compare the opening 7 measures, first without, and then with rubato:
At m. 9 there is greater expressive freedom, with the marking, ad libitum, or in Italian, a piacere (both meaning at your pleasure). Here the 9-note flourish (including the grace-note ornament) should be played without rhythmic counting and as quickly as possible. The measure is written with 16th notes, for notational convenience. Following at m. 10, the marking (in tempo) directs the player to resume the metric count.
Notice the diagonal line between the last two noteheads in m. 9. This is a glissando. The two notes are articulated with one right-hand stroke: the B is played at fret IV which sounds while sliding to C# at fret VI.
A glissando may be played quickly as in the ad libitum measure above, expressed in exact rhythmic timing, or played slowly and freely. The second section of Prayer marked, A little stricter and faster, features a double glissando in both the melody and the bass. These should be rhythmically expressed, so the 2nd notes of the glissandi arrive exactly on the & of 3.
In the final measure, there is a rhythmically free glissando played from the G# which ascends the neck to nothing-ness (in volume and pitch). The 1st finger should remain in contact with the string while the left arm shifts to its higher position to play the XII harmonic on ①. This can be a relatively slow glissando, if a ritard is also taken.
Many of the harmonics in Prayer are played only by the right hand. To sound, extend i, touching the required fret (VII or XII) and stroke the string with p. More about this and glissando can be found in the article One-hand Harmonics and in The Shearer Method Book II, Classic Guitar Developments.