It is useful to classify sight reading into three levels so that we know what we are talking about. At the novice sight reading level, we are talking about playing compositions that we have not memorized, and which we play by looking at the score. We may already be familiar with the melodies in the composition, and have played it before. At the intermediate level, we can sight read music we have never seen or heard before and can sight sing it, although we are not trained in music theory. This level is what is generally considered to be sight reading, and this type of sight reading is the topic of this section. At the advanced level, we are able to apply basic music theory to the sight reading and we are reading music at a much higher level of understanding. How pianists at each of these levels approach sight reading is obviously different. Below, we discuss sight reading rules that are fairly generally applicable.
(1) Keep the eyes on the music; do not look at the keyboard/fingers. You may glance at the hands when it is necessary for large jumps. Try to develop a peripheral vision towards the keyboard so that you have some idea of where the hands are while still looking at the score. Peripheral vision has the advantage that you can keep track of both hands simultaneously. It is particularly beneficial to develop a habit of feeling the keys before playing them. Although this rule applies whether you are sight reading or not, it becomes critical in sight reading. It also helps to "get there ahead of time" for jumps, see section 7.e and 7.f above; therefore, you should practice the jump maneuvers in conjunction with the sight reading practice.
(2) Play through mistakes and make them as inaudible as possible. The best way to do this is to make it sound as if you had modified the music -- then the audience does not know whether you made a mistake or changed it. This is why students with basic music theory training have such an advantage in sight reading. Three ways to make mistakes less audible are (i) keep the rhythm intact, (ii) maintain a continuous melody (if you can't read everything, carry the melody and omit the accompaniment), and (iii) practice simplifying those parts that are too complicated to sight read. The first thing that must be done is to eliminate the habits of stopping and backtracking (stuttering), at every mistake. The best time to develop the skill of not stopping at every mistake is when you begin your first piano lessons. Once the stuttering habit is ingrained, it will take a lot of work to eliminate it. For those with a stuttering habit, the best thing to do is to decide that you will never backtrack again (whether you succeed or not) -- it will slowly go away. Learning to anticipate flubs is a great help, and this will be discussed below. The most powerful tool, is the ability to simplify the music. Eliminate ornamentals, fish out the melody from fast runs, etc.
(3) Learn all the common musical constructs: major and minor scales and their fingerings as well as their corresponding arpeggios, common chords and chord transitions, common trills, ornaments, etc. When sight reading, you should recognize the constructs and not read the individual notes. Memorize the locations of those very high and very low notes as they appear on the score so that you can find them instantly. Start by memorizing all the octave C's, then fill in the others, beginning with notes closest to the C's.
(4) Look ahead of where you are playing; at least one bar ahead, but even more, as you develop the skill at reading the music structure. Get to the point where you can read one structure ahead. By looking ahead, you can not only prepare ahead of time but also anticipate flubs before they occur. You can also anticipate fingering problems and can avoid painting yourself into impossible situations. Although fingering suggestions on the music are generally helpful, they are often useless because, although they may be the best fingerings, you may not be able to use them without some practice. Therefore, you should develop your own set of fingerings just for sight reading.
(5) "Practice, practice, practice". Although sight reading is relatively easy to learn, it must be practiced every day in order to improve. It will take most students from one to two years of diligent practice to become good. Because sight reading depends so heavily on recognition of structures, it is closely related to memory. This means that you can lose the sight reading ability if you stop practicing. However, just as with memory, if you become a good sight reader when young, this ability will stay with you all your life. After practicing sight reading, try to play in your mind (section III.6j), some of the common structures that you encountered.
Of course, you should keep adding to the "tricks of the trade" as you improve. You can acquire the art of scanning through a composition before sight reading it, in order to get some feel for how difficult it is. Then you can figure out ahead of time how to get around the "impossible" sections. You can even practice it quickly, using a condensed version of the learning tricks (HS, shorten difficult segments, use parallel sets, etc.), just enough to make it sound passable. I have met sight readers who would talk to me about some sections of a new piece for a while, then play through it with no trouble. I later figured out that they were practicing those sections in the few seconds they had while they were distracting me with their "discussions".
In order to practice sight reading, you will need to gather several books with many easy pieces and read through them. Because it is initially easier to practice "sight reading" with familiar pieces, you can use the same composition to practice sight reading several times, a week or more apart. There are numerous "Sonatina" books, Mozart's easier sonatas, and books of easy popular songs, are good books for practicing. For the easiest pieces, you might use Beyer, the beginner books listed in III.18c, or the easiest Bach pieces for beginners. Although you can develop a lot of sight reading skills with familiar pieces, you should also practice with pieces that you had never seen before in order to develop true sight reading skills. The most useful skill for help with true sight reading is sight singing, which we now discuss.