When we begin learning a musical instrument for the first time, we have to overcome the initial difficulty of reading music. All tyro instrumentalists must face the challenge sooner or later of learning to read music from the stave. It is, for most, a daunting task; the appearance of lines and dots on a stave might appear alien to begin with. But, if we wish to advance in our instrumental playing, it is a learning curve which we must overcome sooner or later.
Even after the fundamental problem has been mastered--that of recognising and interpreting the notes on the page, we must still make something of the music as a whole. Transforming the two-dimensional codification of rhythm and pitch into actual music, especially when we have had limited or no time to prepare remains immensely troubling for some time--assuming, indeed, that it does not remain a perpetual and lifelong struggle.
Sight-reading is essential for developing genuine musicianship
With any language, be it Spanish, German, Latin, or French, if we only understand the rules (grammar/theory) of the language, but lack the ability to interpolate passage of medium difficulty on the spot, then we will never be truly fluent. The same is true of music. If we can only play a passage musically after months of careful preparation and practice, and always sound like a novice when sight-reading new music, how can we think of ourselves as musicians? And, even if we do so flatter ourselves, can we really expect others to engage in that pretence?
This is why we practise interpreting music at sight. Without that practice, we may be capable of working out a plethora of notes and learning to play a piece of music well, but we may nevertheless be completely lost should we find ourselves unable to take that time. And, in addition, sight-reading trains us to notice more adroitly all the various features of any piece of music, song, or tune. To sight-read well, we must see as much as possible of all the relevant features of the score and read both notes and intervals competently.
If we are unable to do these things, we are like a mathematician who can get the right answer from a simple equation after many hours of intense labour. Just like with the example of other languages, there is no shortcut to fluency in musical language; only years of practise and effort, and many mistakes can give us the confidence and experience to do it well. But the rewards will outstrip the effort put in tenfold.
What are the key skills to work on to improve sight-reading?
As we have already seen, there is more to sight-reading than translating a loose conglomeration of dots on a page into sounds at various pitches. We must consider the interpretation of the piece as a whole, which means its tempo, pulse, key, dynamics, phrasing, and character. As well as interpretation there is also the mechanics, which means focusing our eyes always on the music and not, for instance, on what our fingers happen to be doing at that moment, and, in relation to piano playing, ensuring that our hands are properly positioned to begin with and that we can navigate the keys without looking down all the time.
Interpretation
The first things we always examine upon first seeing a piece of music should be the time signature, key signature, and performance directions. From the time signature, we obtain the pulse--is the piece is 3/4, 6/8, 2/2? This is also important in terms of identifying strong beats and rhythms. It is a good idea to try to tap out the rhythm of a new piece of music, taking each stave's rhythm in each hand respectively. Practise first hands-separately then hands-together. Next, from the key signature we identify the sharps or flats in a piece of music and also its key. See if you can find the major scale which fits the sharps or flats of the key signature, then verify the key by looking at the first base note and checking for accidentals. If the base note is part of the first chord of the scale, it is likely in the major key; otherwise, it may be in the relative minor, which can be found by descending three semitones from the first note of the major scale.
After this, we should look to the tempo, dynamics, and phrasing. The tempo markings can usually be found above the music to the left either in the form of text (often Italian) or metronome marks. They may, for instance, inform us that a piece is to be performed Allegretto, which means quite fast, or tempo di valse, which means simply in the tempo of a waltz. Part of the interpretation of music is performing it in the correct tempo. Dynamics, as well, should be observed beforehand so that the range of different moods expressed through changes in volume can be brought to life during performance. Finally, we have phrasing. A phrase is a musical sentence, often, though not always, represented by a curved line above or below the notes. It is, in essence, a complete unit of musical thought. It is important, therefore, for us to train early to recognise phrases, especially where they are clearly marked. Normally, the end of a musical phrase is demonstrated by a barely perceptible diminuendo and a slight cutting short of the final note. Only with a great deal of practise and attempts to interpret multiple examples of these elements can a musician begin to recognise and sight-read them accurately and reliably. But once they can, they will be much less likely to miss these things in prepared music.
Mechanics
There is not too much to be said on the topic of the mechanics of sight-reading. My instrument is the piano, so what I say I will confine to that instrument. The first commandment here is thou shalt not look at thy fingers. It is a thing which will seem extremely difficult and uncomfortable at first, but which can also become easier very quickly if practised regularly. It requires discipline, but we must force ourselves to look at the music only, and to restart if we falter. The other key thing, and on which the first entirely depends for its success, is prepare thy hands. That means ensure that you have taken account beforehand of where your hands ought to be and any change in position during the piece.
Conclusion
Overall, it is hard to argue with the view that sight-reading is one of the most fundamental skills any musician can develop. Without it, any musician however naturally talented they may be, will flounder. They will learn more slowly than those who have mastered this skill; they will struggle to perform even relatively simple music without laborious preparation; and, most of all, they will most like become frustrated and give up long before they achieve anything close to mastery of their instrument.