If a student wants to have a complete understanding of music, the student should have proper idea of both the theories of music as well as the history of music. Therefore a good faculty should include both theory and history in his or her music lesson plans. As a teacher while you are giving your students lectures on how to read musical notations and know about the various techniques of rhythm such as controlling the tempo successfully, you should also give them an idea on the theory of harmony by including the chords and the key signatures. Also you should give the students a proper idea on how to make a music soothing to the ear. Thus the theories of tone, proper use of dynamics and phrasing should be done.
Also when you are teaching music to your students, proper instructions should be there on the history of the types of music that the student is learning. For example if you are teaching the students western classical music then you must spend some time telling them about the various eras in the western classical music such as the Baroque, Romantic, Classical and so on. If possible then let them have some practical knowledge of the music of that era by bringing in the various types of instruments that were used during these eras.
Thus a student would have better learning about the music of the era once they know the history of the music of that era. It will be even easier for them to play that music on the string instruments. For example, if your students are aware that Baroque instrumental music was closely associated with gavotte and sarabande dance forms and the keyboard music was played on pipe organ and harpsichord then they would be able to perform these pieces quite easily.
Thus you should always have a fair mix of theory and history in your music history lesson plan so that your students can learn in a better way.