Reading Music goes back almost to the beginning of time; just like reading a book, Music learns the notation with letters and sentences. However, reading Music is more complex because you have to understand the rhythmic structures to note values, measure counting, and practicing scales and arpeggios for your principal instrument.
Furthermore, each tool is different for reading Music; fundamental principles to know first are:
Composition & Form - Structural construct for creating and processing an composition. Reading music for anyone getting to know how the musical piece is organized, should know basic forms, such as; A, B, A = melody and theme, variety, back to the theme.
Notation - This is recognizing symbols such as; the staff, ledger line positioning, keys, and loud and soft markings.
Note Consideration - After recognizing what makes up musical phrases, and what timbre sounds are included; value in notes, omitted notes by rests, one can determine the sounds of Music.
Two basic principles make up the structure of Music; the rhythmic function, and chordal and scale procedures.
Rhythmic functions - The chart above denotes note values in sequence, but by putting them in a musical sentence makes little sense without harmonic chord structure,
Scale procedures to chords - Practicing scales and modal scales can be recognized in reading music as a valuable aid for sight-reading. Furthermore, by knowing scales you can recognize notes in chord structures which dominate the musical sentence. An example would be I-IV7-V-I, an ending in most compositions.
Reading music in orchestras, choirs, and bands; a string player, singer, and instrumentalist must have a understanding and knowledge of all the above principles. This takes experience with teachers who teach voice methods and conductors who takes singers to read music for performance. All string, brass, and percussion players have to be acquainted with their own particular notations in reading music in a group situation. However, to read music is a skill demanded from a person perform music.